[red-knot] simplify type lookup in function/class definitions #35572

Job	Run time
Determine changes	13s
mkdocs	2m 48s
pre-commit	38s
cargo fmt	18s
python package	1m 16s
cargo build (release)	5m 46s
cargo build (msrv)	3m 54s
benchmarks	5m 13s
cargo clippy	1m 56s
cargo fuzz	5m 2s
cargo shear	25s
cargo test (wasm)	1m 39s
cargo test (linux)	4m 2s
cargo test (windows)	8m 24s
test scripts	1m 8s
formatter instabilities and black similarity	0s
test ruff-lsp	46s
ecosystem	8m 59s
Fuzz the parser	0s
	52m 27s

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