Refactor filtering to deduplicate logic before bugfixes. #1727

Job	Run time
Check lint and rustfmt	37s
Run JS linters	44s
Check rustdoc WASM target	19s
Check fuzz targets	11s
Run tests	48s
WASM tests	1m 38s
Python tests and maturin build (3.9)	45s
pre-publish checks	0s
Python tests and maturin build (3.10)	42s
Python tests and maturin build (3.11)	34s
Python tests and maturin build (3.12)	40s
Python tests and maturin build (3.13.0-rc - 3.13)	1m 0s
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 59s

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