Refactor and clean up filter validity logic. #1573

Job	Run time
Check lint and rustfmt	31s
Run JS linters	48s
Check rustdoc WASM target	20s
Check fuzz targets	13s
Run tests	1m 0s
Python tests and maturin build (3.9)	44s
WASM tests	1m 31s
Python tests and maturin build (3.10)	53s
pre-publish checks	0s
Python tests and maturin build (3.11)	41s
Python tests and maturin build (3.12)	35s
All CI stages	1s
pre-publish checks	0s
publish trustfall_filetests_macros	0s
publish trustfall_core	0s
publish trustfall_derive	0s
publish python trustfall	0s
publish trustfall	0s
publish trustfall_stubgen	0s
	7m 17s

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