add a basic benchmark for DeepCollectionEquality

[jakemac53]

I wanted to check the performance impact of using .entries instead of .keys followed by a lookup, so I wrote this.

Will send out that PR separately - spoiler alert we might not want to land it 🤣 .

[github-actions[bot]]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:characters	1.4.0	ready to publish	characters-v1.4.0
package:args	2.6.1-wip	WIP (no publish necessary)
package:async	2.12.0	already published at pub.dev
package:collection	1.19.1	already published at pub.dev
package:convert	3.1.2	already published at pub.dev
package:crypto	3.0.6	already published at pub.dev
package:fixnum	1.1.1	already published at pub.dev
package:logging	1.3.0	already published at pub.dev
package:os_detect	2.0.3-wip	WIP (no publish necessary)
package:path	1.9.1	already published at pub.dev
package:platform	3.1.6	already published at pub.dev
package:typed_data	1.4.0	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions[bot]]

PR Health

Breaking changes :heavy_check_mark:

| Package | Change | Current Version | New Version | Needed Version | Looking good? | | :--- | :--- | ---: | ---: | ---: | ---: | |collection|None|1.19.1|1.19.1|1.19.1|:heavy_check_mark:|

Coverage :warning:

| File | Coverage | | :--- | :--- | |pkgs/collection/benchmark/deep_collection_equality.dart| :broken_heart: Not covered | This check for [test coverage](https://github.com/dart-lang/ecosystem/wiki/Test-Coverage) is informational (issues shown here will not fail the PR). This check can be disabled by tagging the PR with `skip-coverage-check`.

API leaks :heavy_check_mark:

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API. | Package | Leaked API symbols | | :--- | :--- |

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