feat(macros): support using #[dynify] on remote items

[loichyan]

Support using #[dynify] on remote items (either a trait or a function):

#[dynify(remote = "external_crate::Read")]
pub(crate) trait DynRead {
    async fn read_to_string(&mut self) -> String;
}

Note that the syntax for specifying arbitrary tokens as the value of an option of #[dynify] follows those used in serde.

[codecov]

Codecov Report

❌ Patch coverage is 94.33962% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.09%. Comparing base (1474e09) to head (030f33a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib.rs	0.00%	2 Missing ⚠️
macros/src/dynify.rs	98.03%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
- Coverage   98.37%   98.09%   -0.28%     
==========================================
  Files          12       13       +1     
  Lines         862      893      +31     
==========================================
+ Hits          848      876      +28     
- Misses         14       17       +3     

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