perf: fast comparison using `FullSpan` and source code #319

Job	Run time
Builds Playground	59s
Check Formatting	16s
Check TODOs	9s
Test CSharpier.MSBuild (windows-latest)	1m 28s
Test CSharpier.MSBuild (ubuntu-latest)	1m 26s
No Warnings	50s
Run Tests	1m 17s
	6m 25s

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