Implement separate augmentation phase for Cargo packages

[cottsay]

In addition to moving non-identity package metadata out of the CargoPackageIdentification extension and into a new CargoPackageAugmentation extension, this change also:

1. Converts dependencies to use the DependencyDescriptor type
2. Adds "author" metadata to colcon's "maintainer" metadata
3. Interprets unspecified versions as 0.0.0 (per cargo docs)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 72.91667% with 13 lines in your changes missing coverage. Please review.

Project coverage is 68.07%. Comparing base (48a4245) to head (dd3815e).

Files with missing lines	Patch %	Lines
colcon_cargo/package_augmentation/cargo.py	78.37%	3 Missing and 5 partials ⚠️
colcon_cargo/package_identification/cargo.py	54.54%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
+ Coverage   67.20%   68.07%   +0.87%     
==========================================
  Files           6        7       +1     
  Lines         247      260      +13     
  Branches       37       44       +7     
==========================================
+ Hits          166      177      +11     
+ Misses         57       55       -2     
- Partials       24       28       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[luca-della-vedova]

Thanks! I created a small PR targeting your branch to test the new feature and make sure we keep a good coverage #49

[cottsay]

Thank you for adding tests! This PR now has a net improvement on overall project coverage, but more importantly, the metadata being read is now actually verified.