perf: cache `IgnoreWithBasePath` #320

Job	Run time
Check Formatting	15s
Builds Playground	1m 4s
Check TODOs	6s
Test CSharpier.MSBuild (ubuntu-latest)	1m 41s
No Warnings	53s
Run Tests	1m 7s
Test CSharpier.MSBuild (windows-latest)	1m 43s
	6m 49s

Provide feedback