feat(impls): add rust_decimal::Decimal impl

[seanpianka]

Goal

Provide a serde-based implementation of TS for rust_decimal::Decimal
Closes #272

Changes

Derive an implementation for rust_decimal::Decimal using feature flag serde-with-str.

Checklist

• I have followed the steps listed in the Contributing guide.
• If necessary, I have added documentation related to the changes made.
• I have added or updated the tests related to the changes made.

[escritorio-gustavo]

Hey, thanks for the PR! Please check out the Contributing guide for instructions on how to update the README.

Edit: I see the link in the PR template is incorrectly pointing at the CHANGELOG file instead of CONTRIBUTING, sorry about that, it's already been fixed, both in the template and in this PR's description

[NyxCode]

I'm a bit confused by rust-decimal in general. Their usage of features seems a bit odd to me (though we're abusing them similarly I guess).

If we want support rust-decimal going forward, I think we need to seamlessly support all these modes - and I'm not sure that's easily possible.

Re-exposing all features of rust_decimal, for example, doesn't seem great.
rust_decimal already has feature gates for a wide variety of libraries, so maybe it'd be worth a shot to open a PR there. In the rust_decimal crate, this could be implemented nicely using #[cfg(feature = "..")] annotations.

[NyxCode]

Closing this for now. I think we established that we can't support this properly.
Either rust_decimal implements TS behind a feature-flag, or users will have to use #[ts(as = ..)] or #[ts(type = "..")].