[red-knot] Remove `Type::Unbound` #34661

Job	Run time
mkdocs	2m 43s
cargo fmt	15s
Determine changes	12s
pre-commit	36s
python package	1m 17s
benchmarks	4m 4s
cargo build (release)	4m 52s
cargo clippy	1m 12s
cargo build (msrv)	3m 18s
cargo fuzz	4m 33s
cargo shear	26s
cargo test (linux)	3m 5s
cargo test (wasm)	1m 35s
cargo test (windows)	7m 50s
test scripts	1m 0s
formatter instabilities and black similarity	0s
Fuzz the parser	0s
ecosystem	0s
test ruff-lsp	0s
	36m 58s

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