[red-knot] Minor simplifications and improvements to constraint narrowing logic #38239

Job	Run time
mkdocs	2m 23s
Determine changes	12s
cargo fmt	19s
cargo build (release)	0s
pre-commit	3m 3s
python package	1m 20s
cargo fuzz build	5m 3s
cargo build (msrv)	4m 2s
benchmarks	4m 55s
cargo clippy	1m 53s
cargo shear	25s
cargo test (linux)	1m 52s
cargo test (linux, release)	3m 54s
cargo test (wasm)	1m 45s
cargo test (windows)	2m 55s
formatter instabilities and black similarity	0s
test scripts	59s
ecosystem	2m 38s
test ruff-lsp	35s
fuzz parser	0s
	38m 13s

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