feat: add functional equivalent of Array.prototype.copyWithin and TypedArray.prototype.copyWithin

lib/node_modules/@stdlib/utils/copy-within/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.
+
+-->
+
+# copyWithin
+
+> Copy a sequence of elements within a collection to another location in the same collection.
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- Package usage documentation. -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var copyWithin = require( '@stdlib/utils/copy-within' );
+```
+
+#### copyWithin( collection, target\[, start\[, end]] )
+
+Copies a sequence of elements within a collection to another location in the same collection.
+
+```javascript
+var arr = [ 1, 2, 3, 4, 5 ];
+
+var out = copyWithin( arr, 0, 3 );
+// returns [ 4, 5, 3, 4, 5 ]
+```
+
+The function accepts the following arguments:
+
+-   **collection**: the input collection.
+-   **target**: target index (zero-based).
+-   **start**: source start index (zero-based). Default: 0.
+-   **end**: source end index (zero-based, non-inclusive). Default: collection.length.
+
+If a provided collection has a built-in `copyWithin` method (e.g., [Array.prototype.copyWithin][mdn-copy-within] or [TypedArray.prototype.copyWithin][mdn-typed-array-copy-within]), the function defers to that method. Otherwise, the function provides a polyfill, thus extending `copyWithin` support to environments lacking the built-in API for Array and TypedArray.
+
+The function supports negative indices, which are interpreted as being relative to the end of the collection. For example, if provided `-2` for `target`, the function interprets the index as `collection.length - 2`.
+
+```javascript
+var arr = [ 1, 2, 3, 4, 5 ];
+
+var out = copyWithin( arr, -2, -3, -1 );
+// returns [ 1, 2, 3, 3, 4 ]
+```
+
+If `target` is greater than or equal to the collection length, nothing is copied. If `target` is positioned after `start` after normalization, copying only happens until the end of the collection length (in other words, `copyWithin` never extends the collection).
+
+```javascript
+var arr = [ 1, 2, 3, 4, 5 ];
+
+var out = copyWithin( arr, 10, 0 );
+// returns [ 1, 2, 3, 4, 5 ]
+```
+
+If `start` is greater than or equal to the collection length, nothing is copied.
+
+```javascript
+var arr = [ 1, 2, 3, 4, 5 ];
+
+var out = copyWithin( arr, 0, 10 );
+// returns [ 1, 2, 3, 4, 5 ]
+```
+
+For Uint8Array inputs, the function uses an optimized implementation that copies in 4-byte increments when possible, providing better performance for large arrays.
+
+</section>
+
+<!-- /.usage -->
+
+<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+## Notes
+
+-   The function works like the built-in `Array.prototype.copyWithin` and `TypedArray.prototype.copyWithin` methods but extends support to all collection types.
+
+</section>
+
+<!-- /.notes -->
+
+<!-- Package usage examples. -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var copyWithin = require( '@stdlib/utils/copy-within' );
+
+// Regular arrays:
+var arr = [ 1, 2, 3, 4, 5 ];
+console.log( copyWithin( arr, 0, 3 ) );
+// => [ 4, 5, 3, 4, 5 ]
+
+arr = [ 1, 2, 3, 4, 5 ];
+console.log( copyWithin( arr, 0, 3, 4 ) );
+// => [ 4, 2, 3, 4, 5 ]
+
+arr = [ 1, 2, 3, 4, 5 ];
+console.log( copyWithin( arr, -2, -3, -1 ) );
+// => [ 1, 2, 3, 3, 4 ]
+
+// Typed arrays:
+var Uint8Array = require( '@stdlib/array/uint8' );
+var typed = new Uint8Array( [ 1, 2, 3, 4, 5 ] );
+console.log( copyWithin( typed, 0, 3 ) );
+// => <Uint8Array>[ 4, 5, 3, 4, 5 ]
+
+// Array-like objects:
+var obj = {
+    'length': 5,
+    '0': 1,
+    '1': 2,
+    '2': 3,
+    '3': 4,
+    '4': 5
+};
+console.log( copyWithin( obj, 0, 3 ) );
+// => { '0': 4, '1': 5, '2': 3, '3': 4, '4': 5, 'length': 5 }
+```
+
+</section>
+
+<!-- /.examples -->
+
+<section class="references">
+
+</section>
+
+<!-- /.references -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+* * *
+
+## See Also
+
+-   <span class="package-name">[`@stdlib/utils/copy`][@stdlib/utils/copy]</span><span class="delimiter">: </span><span class="description">copy or deep clone a value to an arbitrary depth.</span>
+
+</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">
+
+[mdn-copy-within]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin
+[mdn-typed-array-copy-within]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray/copyWithin
+
+<!-- <related-links> -->
+
+[@stdlib/utils/copy]: https://github.com/stdlib-js/utils-copy
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->