style: align dstructs/compact-adjacency-matrix with namespace conventions

Added missing `benchmark/benchmark.js` (present in 87.5% of `dstructs`
siblings) with an instantiation-only scaffold matching the boilerplate
used by sibling benchmarks (Apache header, `format()`-based bench label,
`b.tic`/`b.toc`/`b.pass`/`b.end`); added `directories.benchmark` entry
to `package.json` (present in 87.5% of siblings).

https://claude.ai/code/session_01Y3Xf8psrX9CDj1KvW8f9xC

Author: claude

lib/node_modules/@stdlib/dstructs/compact-adjacency-matrix/benchmark/benchmark.js

@@ -0,0 +1,71 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2026 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';
+
+// MODULES //
+
+var bench = require( '@stdlib/bench' );
+var instanceOf = require( '@stdlib/assert/instance-of' );
+var format = require( '@stdlib/string/format' );
+var pkg = require( './../package.json' ).name;
+var CompactAdjacencyMatrix = require( './../lib' );
+
+
+// MAIN //
+
+bench( format( '%s::instantiation,new', pkg ), function benchmark( b ) {
+	var adj;
+	var i;
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		adj = new CompactAdjacencyMatrix( 10 );
+		if ( typeof adj !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !instanceOf( adj, CompactAdjacencyMatrix ) ) {
+		b.fail( 'should return an instance' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});
+
+bench( format( '%s::instantiation,no_new', pkg ), function benchmark( b ) {
+	var compactAdjacencyMatrix;
+	var adj;
+	var i;
+
+	compactAdjacencyMatrix = CompactAdjacencyMatrix;
+
+	b.tic();
+	for ( i = 0; i < b.iterations; i++ ) {
+		adj = compactAdjacencyMatrix( 10 );
+		if ( typeof adj !== 'object' ) {
+			b.fail( 'should return an object' );
+		}
+	}
+	b.toc();
+	if ( !instanceOf( adj, CompactAdjacencyMatrix ) ) {
+		b.fail( 'should return an instance' );
+	}
+	b.pass( 'benchmark finished' );
+	b.end();
+});

lib/node_modules/@stdlib/dstructs/compact-adjacency-matrix/package.json

@@ -15,6 +15,7 @@
   ],
   "main": "./lib",
   "directories": {
+    "benchmark": "./benchmark",
     "doc": "./docs",
     "example": "./examples",
     "lib": "./lib",