feat: add doctest-annotation-spacing ESLint rule

lib/node_modules/@stdlib/_tools/eslint/rules/doctest-annotation-spacing/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2025 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# doctest-annotation-spacing
+
+> [ESLint rule][eslint-rules] to enforce spacing in return annotations in single-line comments.
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var rule = require( '@stdlib/_tools/eslint/rules/doctest-annotation-spacing' );
+```
+
+#### rule
+
+[ESLint rule][eslint-rules] to enforce spacing in return annotations in single-line comments. The rule checks `// returns` and `// =>` annotations (including `// e.g., returns` and `// e.g., =>` variants) and ensures:
+
+-   Exactly 1 space between `//` and the annotation keyword
+-   Exactly 1 space after the annotation keyword
+
+**Bad** (too many spaces after `returns`):
+
+<!-- eslint-disable stdlib/doctest-annotation-spacing -->
+
+```javascript
+var v = 3.14;
+// returns             3.14
+```
+
+**Bad** (no space before `=>`):
+
+<!-- eslint-disable stdlib/doctest-annotation-spacing, spaced-comment -->
+
+```javascript
+console.log( 'beep' );
+//=> 'beep'
+```
+
+**Bad** (too many spaces before `returns`):
+
+<!-- eslint-disable stdlib/doctest-annotation-spacing, spaced-comment -->
+
+```javascript
+var x = true;
+//  returns true
+```
+
+**Good**:
+
+```javascript
+var v = 3.14;
+// returns 3.14
+
+console.log( 'beep' );
+// => 'beep'
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   This rule only applies to single-line comments (starting with `//`). Multi-line comments (`/* ... */`) are ignored.
+
+-   The rule matches the following patterns:
+
+    -   `// returns`
+    -   `// =>`
+    -   `// e.g., returns`
+    -   `// e.g., =>`
+
+-   The rule enforces two spacing requirements:
+
+    -   Exactly 1 space after `//`
+    -   Exactly 1 space after the keyword
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var Linter = require( 'eslint' ).Linter;
+var rule = require( '@stdlib/_tools/eslint/rules/doctest-annotation-spacing' );
+
+var linter = new Linter();
+
+var code = [
+    'var v = foo();',
+    '// returns             \'beep\'',
+    '',
+    'console.log( bar() );',
+    '// => \'boop\''
+].join( '\n' );
+
+linter.defineRule( 'doctest-annotation-spacing', rule );
+
+var result = linter.verify( code, {
+    'rules': {
+        'doctest-annotation-spacing': 'error'
+    }
+});
+/* returns
+    [
+        {
+            'ruleId': 'doctest-annotation-spacing',
+            'severity': 2,
+            'message': 'Return annotation keyword `returns` should be followed by 1 space. Found 13 space(s).',
+            'line': 2,
+            'column': 1,
+            'nodeType': null,
+            'endLine': 2,
+            'endColumn': 30
+        }
+    ]
+*/
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[eslint-rules]: https://eslint.org/docs/developer-guide/working-with-rules
+
+</section>
+
+<!-- /.links -->

lib/node_modules/@stdlib/_tools/eslint/rules/doctest-annotation-spacing/examples/index.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+var Linter = require( 'eslint' ).Linter;
+var rule = require( './../lib' );
+
+var linter = new Linter();
+
+var code = [
+	'var v = foo();',
+	'// returns             \'beep\'',
+	'',
+	'console.log( bar() );',
+	'// => \'boop\''
+].join( '\n' );
+
+linter.defineRule( 'doctest-annotation-spacing', rule );
+
+var result = linter.verify( code, {
+	'rules': {
+		'doctest-annotation-spacing': 'error'
+	}
+});
+console.log( result );
+/* =>
+	[
+		{
+			'ruleId': 'doctest-annotation-spacing',
+			'severity': 2,
+			'message': 'Return annotation keyword `returns` should be followed by 1 space(s). Found 13 space(s).',
+			'line': 2,
+			'column': 1,
+			'nodeType': null,
+			'endLine': 2,
+			'endColumn': 30
+		}
+	]
+*/

lib/node_modules/@stdlib/_tools/eslint/rules/doctest-annotation-spacing/lib/index.js

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+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2025 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+/**
+* ESLint rule to enforce spacing after return annotations in single-line comments.
+*
+* @module @stdlib/_tools/eslint/rules/doctest-annotation-spacing
+*
+* @example
+* var rule = require( '@stdlib/_tools/eslint/rules/doctest-annotation-spacing' );
+*
+* console.log( rule );
+*/
+
+// MODULES //
+
+var main = require( './main.js' );
+
+
+// EXPORTS //
+
+module.exports = main;