Consider using package.metadata to configure allow/warn/deny/forbid lint settings

[obi1kenobi]

While we wait for external tools support for the lints table, consider using package.metadata to allow crates to configure their lint settings.

For example, this could address the tokio use case where they'd prefer to allow minor lints like #[must_use]. It would also allow us to add allow-by-default lints like "API got extended," which may be desirable for some use cases and not desirable in others.

Docs: https://doc.rust-lang.org/cargo/reference/manifest.html#the-metadata-table

[pksunkara]

Related issue: #58

[obi1kenobi]

This has been implemented for a little while: https://github.com/obi1kenobi/cargo-semver-checks?tab=readme-ov-file#lint-level-configuration

We just forgot to close the issue. Closing!