ci: foundry multibuild workflow

[PaulRBerg]

This PR adds a CI workflow that runs once weekly to use my Foundry Multibuild action for checking that Forge Std remains compatible with all compiler versions allowed by the pragma (from v0.6.2 up to v0.8.23).

Notes:

• Some files likeconsole.sol use >=0.4.22, but Foundry Multibuild does not work with a pragma so low because the other files wouldn't compile.
• Tests are excluded because they are not meant to be used by consumers of Forge Std (and they wouldn't work anyway for the same reason as above)
• For more details on Foundry Multibuild, see my announcement on Twitter, and the GitHub repo.

[mds1]

Nice github action, that's really handy!

For forge-std, I don't think we should merge this to avoid introducing unnecessary dependencies, since we already rolled our own solution for this here (we could probably simplify that by removing the manual stdout parsing now that forge has --deny-warnings, but that's tangential)

Two small suggestions for Foundry Multibuild would be adding flags for skip-script and supporting forge's --deny-warnings option :)

[PaulRBerg]

Thanks, @mds1!

For forge-std, I don't think we should merge this to avoid introducing unnecessary dependencies

Makes sense

we already rolled our own solution for this here

Oh, I missed that.

Two small suggestions for Foundry Multibuild would be adding flags for skip-script and supporting forge's --deny-warnings option :)

Those are great ideas - I've created issues to track them.