Improved migration performance, better error reporting, and other cleanups

[gwynne]

• FluentError is now CustomDebugStringConvertible
• Fixes #542 by conditionally conforming LoggingOverrideDatabase to SQLDatabase
• Migration no longer spends time checking for prerelease migration names or allocating excess futures
• The Mirror bypass is now enabled for Swift 5.9
• Fluent benchmark suite now has much better error handling
• Fluent benchmarks now run ~5-10% faster (up to 15% for SQL databases)

[codecov-commenter]

Codecov Report

Merging #563 (01fd1ff) into main (559dc9c) will increase coverage by 0.15%. The diff coverage is 7.14%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #563 +/- ## ========================================== + Coverage 46.75% 46.91% +0.15% ========================================== Files 106 106 Lines 6239 6201 -38 ========================================== - Hits 2917 2909 -8 + Misses 3322 3292 -30 ``` | [Impacted Files](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor) | Coverage Δ | | |---|---|---| | [Sources/FluentKit/Database/Databases.swift](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRGF0YWJhc2UvRGF0YWJhc2VzLnN3aWZ0) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/Migration/Migrator.swift](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvTWlncmF0aW9uL01pZ3JhdG9yLnN3aWZ0) | `0.00% <0.00%> (ø)` | | | [Sources/FluentKit/FluentError.swift](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRmx1ZW50RXJyb3Iuc3dpZnQ=) | `18.64% <11.11%> (-2.93%)` | :arrow_down: | | [Sources/FluentKit/Database/Database+Logging.swift](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvRGF0YWJhc2UvRGF0YWJhc2UrTG9nZ2luZy5zd2lmdA==) | `31.42% <28.57%> (-5.24%)` | :arrow_down: | | [Sources/FluentKit/Model/MirrorBypass.swift](https://codecov.io/gh/vapor/fluent-kit/pull/563?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vapor#diff-U291cmNlcy9GbHVlbnRLaXQvTW9kZWwvTWlycm9yQnlwYXNzLnN3aWZ0) | `76.71% <75.00%> (-7.50%)` | :arrow_down: |

[VaporBot]

These changes are now available in 1.42.1