Add very limited support for `#[builder(const)]` #940

Job	Run time
compilation-benchmarks	2m 5s
cargo-lock	8s
test-msrv (ubuntu, 1.59.0)	1m 5s
test-unstable (beta, --locked)	27s
cargo-doc (ubuntu)	21s
test-unstable (beta)	31s
test-msrv (ubuntu, 1.61.0)	1m 0s
test-unstable (nightly, --locked)	25s
cargo-doc (windows)	2m 17s
test-msrv (windows, 1.59.0)	1m 40s
test-unstable (nightly)	26s
cargo-doc (macos)	33s
test-msrv (windows, 1.61.0)	1m 46s
cargo-fmt	15s
test-msrv (macos, 1.59.0)	56s
cargo-machete	3s
cargo-miri (--locked)	1m 48s
cargo-miri	1m 46s
test-msrv (macos, 1.61.0)	1m 1s
prettier	6s
taplo-fmt	4s
typos	5s
website-build	23s
version-sync	3s
runtime-benchmarks (args_3)	1m 13s
runtime-benchmarks (args_5)	52s
test-stable (ubuntu, --locked)	1m 25s
runtime-benchmarks (args_10_alloc)	1m 21s
test-stable (ubuntu)	1m 26s
runtime-benchmarks (args_10_structs)	1m 9s
test-stable (windows, --locked)	3m 2s
runtime-benchmarks (args_10)	1m 1s
test-stable (windows)	5m 24s
runtime-benchmarks (args_20)	58s
test-stable (macos, --locked)	1m 10s
test-stable (macos)	1m 11s
	39m 26s

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