ci: Add docs.rs build to publish

[febo]

Problem

As described on #411 , docs.rs build failed after publishing the crate since it uses a nightly toolchain where doc_auto_cfg feature has been removed.

Solution

This PR adds a job to the publish workflow to build the documentation using docs.rs image and a nightly toolchain.

A successful run of the job can be seen here: https://github.com/febo/solana-sdk/actions/runs/18941243715/job/54080342807

[joncinque]

Looks good to me! I couldn't find any more documentation about the exact command they use, but this looks close enough. I tried running the cargo command on its own on a crate with the docs_auto_cfg feature, and it failed as expected, so that should do what we need.

We could potentially eliminate the whole docker setup if you want to simplify a bit more and just call cargo +nightly ... directly, that worked equally well for me.

We'll need to update the proc-macro2 dependency in our lockfile, because the docs build fails locally for me.

[joncinque]

I'm not sure if you ran this command successfully on your machine, but on mine, I need to quote all of the env declarations

Suggested change

	-e CARGO_HOME=/cargo \
	-e RUSTUP_HOME=/rustup \
	-e PATH=/cargo/bin:$PATH \
	-e DOCS_RS=1 \
	-e RUSTDOCFLAGS="--cfg docsrs" \
	-e "CARGO_HOME=/cargo" \
	-e "RUSTUP_HOME=/rustup" \
	-e "PATH=/cargo/bin:$PATH" \
	-e "DOCS_RS=1" \
	-e "RUSTDOCFLAGS=\"--cfg docsrs\"" \

[febo]

We could potentially eliminate the whole docker setup if you want to simplify a bit more and just call cargo +nightly ... directly, that worked equally well for me.

Agree , I think it is sufficient to run cargo +nightly doc. Here is an example run: https://github.com/febo/solana-sdk/actions/runs/18959537456/job/54143821569

We'll need to update the proc-macro2 dependency in our lockfile, because the docs build fails locally for me.

Hmmm, I ran cargo +nightly doc --no-deps --all-features locally from the root and it succeeds.

[joncinque]

Hmmm, I ran cargo +nightly doc --no-deps --all-features locally from the root and it succeeds.

Alright, let's roll the dice and see what happens!