feat(`forge doc`): include custom natspec #15961

Job	Run time
crate-checks	2m 49s
docs	1m 19s
codespell	8s
clippy	1m 29s
doctest	2m 35s
forge-fmt	1m 27s
rustfmt	14s
nextest / build matrices	6s
nextest / test unit (x86_64-unknown-linux-gnu)	3m 26s
nextest / test integration (1/3) (x86_64-unknown-linux-gnu)	6m 47s
nextest / test integration (2/3) (x86_64-unknown-linux-gnu)	7m 9s
nextest / test integration (3/3) (x86_64-unknown-linux-gnu)	6m 29s
nextest / test integration / issue-repros (1/2) (x86_64-unknown-linux-gnu)	6m 9s
nextest / test integration / issue-repros (2/2) (x86_64-unknown-linux-gnu)	7m 21s
nextest / test integration / external (1/2) (x86_64-unknown-linux-gnu)	10m 57s
nextest / test integration / external (2/2) (x86_64-unknown-linux-gnu)	7m 22s
nextest / test unit (x86_64-pc-windows-msvc)	10m 29s
nextest / test integration (1/3) (x86_64-pc-windows-msvc)	10m 29s
nextest / test integration (2/3) (x86_64-pc-windows-msvc)	13m 18s
nextest / test integration (3/3) (x86_64-pc-windows-msvc)	10m 57s
ci-success	4s
	1h 51m 4s

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