General cleanup

[gwynne]

These changes are now available in 4.10.0

The usual: Bump the Swift minimum to 5.10, update CI, update the README, update the API docs theme, update dependency minimums, and clean up the tests.

Special thanks to @Freelenzer for pointing out the need to bump the AsyncKit minimum!

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 68.37%. Comparing base (ac03d7c) to head (fbf7695).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/MySQLKit/MySQLDialect.swift	40.00%	3 Missing ⚠️
Sources/MySQLKit/MySQLDatabase+SQL.swift	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #330      +/-   ##
==========================================
+ Coverage   66.46%   68.37%   +1.91%     
==========================================
  Files           9        9              
  Lines         325      332       +7     
==========================================
+ Hits          216      227      +11     
+ Misses        109      105       -4     

Files with missing lines	Coverage Δ
Sources/MySQLKit/MySQLDatabase+SQL.swift	41.66% <0.00%> (-35.76%)	⬇️
Sources/MySQLKit/MySQLDialect.swift	73.21% <40.00%> (+5.41%)	⬆️

... and 6 files with indirect coverage changes

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