feat: use equivalent to loose the key trait bounds

[MrCroxx]

Signed-off-by: MrCroxx [email protected]## What's changed and what's your intention?

Please explain IN DETAIL what the changes are in this PR and why they are needed. :D

See examples/equivalent.rs for usage. 🥵

This PR modifies the public API trait bounds, but only looses them. So, there is no need to bump a major version. 🥵

Checklist

• I have written the necessary rustdoc comments
• I have added the necessary unit tests and integration tests
• I have passed make all (or make fast instead if the old tests are not modified) in my local environment.

Related issues or PRs (optional)

close #378

[codecov]

Codecov Report

Attention: Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
foyer-memory/src/generic.rs	66.66%	2 Missing ⚠️

Files with missing lines	Coverage Δ
foyer-memory/src/cache.rs	84.55% <ø> (-0.04%)	⬇️
foyer-memory/src/indexer/hash_table.rs	100.00% <100.00%> (ø)
foyer-memory/src/indexer/sanity.rs	100.00% <100.00%> (ø)
foyer-storage/src/store.rs	85.23% <100.00%> (-0.11%)	⬇️
foyer-storage/src/test_utils.rs	88.46% <100.00%> (-0.22%)	⬇️
foyer/src/hybrid/cache.rs	82.33% <100.00%> (-0.39%)	⬇️
foyer-memory/src/generic.rs	90.79% <66.66%> (+0.21%)	⬆️