feat: add ErrFactory type to err.ts.

Using Err in some other libraries has led to a proliferation of
slow-type errors related to exported const error factories. This should
help resolve that issue.

Author: baetheus

deno.json

@@ -1,6 +1,6 @@
 {
   "name": "@baetheus/fun",
-  "version": "3.0.0-rc.5",
+  "version": "3.0.0-rc.6",
   "exports": {
     "./applicable": "./applicable.ts",
     "./array": "./array.ts",

err.ts

@@ -48,6 +48,17 @@ export type Err<T extends string, A> = {
 // deno-lint-ignore no-explicit-any
 export type AnyErr = Err<string, any>;
 
+/**
+ * A type alias for an Err factory returned by the err function. This is useful
+ * to combat deno slow-types errors on publish.
+ *
+ * @since 3.0.0-rc.6
+ */
+export type ErrFactory<T extends string> = <A>(
+  message: string,
+  context?: A,
+) => Err<T, A>;
+
 /**
  * Create a constructor function for a specific error type.
  *
@@ -67,7 +78,7 @@ export type AnyErr = Err<string, any>;
  */
 export function err<T extends string>(
   name: T,
-): <A>(message: string, context?: A) => Err<T, A> {
+): ErrFactory<T> {
   return (message, context) => ({
     tag: "Error",
     name,