refactor: replace manual future enum with auto_enum

[MrCroxx]

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

As title.

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)

[codecov]

Codecov Report

Attention: Patch coverage is 11.76471% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
foyer-storage/src/engine.rs	20.00%	8 Missing ⚠️
foyer-storage/src/storage/either.rs	0.00%	7 Missing ⚠️

Files with missing lines	Coverage Δ
foyer-storage/src/storage/either.rs	0.00% <0.00%> (ø)
foyer-storage/src/engine.rs	31.13% <20.00%> (-3.33%)	⬇️