parser: remove Regexes from whitespace parser #574

Job	Run time
lint	2m 49s
docs	2m 40s
coverage	6m 7s
Rust unit tests (ubuntu-latest)	3m 2s
Rust unit tests (macos-latest)	2m 30s
Rust unit tests (windows-latest)	3m 19s
Rustfmt	21s
typecheck	2m 25s
test (macos-latest, 3.8)	7m 40s
test (macos-latest, 3.9)	7m 58s
test (macos-latest, 3.10)	8m 3s
test (macos-latest, 3.11)	8m 1s
test (macos-latest, 3.12-dev)	12m 8s
test (ubuntu-latest, 3.8)	5m 51s
test (ubuntu-latest, 3.9)	6m 52s
test (ubuntu-latest, 3.10)	7m 4s
test (ubuntu-latest, 3.11)	5m 54s
test (ubuntu-latest, 3.12-dev)	7m 16s
test (windows-latest, 3.8)	7m 16s
test (windows-latest, 3.9)	7m 16s
test (windows-latest, 3.10)	9m 4s
test (windows-latest, 3.11)	11m 13s
test (windows-latest, 3.12-dev)	12m 33s
	2h 27m 22s

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