feat: Support multiple crates in check-downstream-compiles

[samuelburnham]

Optionally takes in the more-paths input, which will take the same Cargo.toml path patches for the initially patched crate and apply them to each specified crate further down the stack.

For example, argumentcomputer/Plonky3#6 shows:

• Plonky3 calls the downstream action and is the source of path patches
• Sphinx is the primary crate to be patched & checked, and saves its relevant patches to patches.txt
• Zk-light-clients is the secondary crate to be patched & check, which it does by simply writing the patches in patches.txt to each Cargo.toml file in the repo.
• More paths downstream of Sphinx could be specified, so long as they are checked out to a separate path in the caller repo.

Note

This PR should be merged before argumentcomputer/Plonky3#6, as the latter currently depends on the downstream-transitive branch here.

[wwared]

This looks good, I just want to remind about this comment because we keep adding more inscrutable sed lines to this workflow.

But it makes sense and it seems to work, thanks!