Fix warnings for bakery and improve Pydantic usage

[ianpittwood]

Takes our pytest warnings from 94 to 0.

• Fix warnings about unclosed file handles.
• Fix a bug (and warning) where snyk monitor calls without tags would cause the validator to throw back a Nonetype.
• Fixes the before model validator in ManifestBuild to be the correct usage.
• Improve type hints across multiple models.
  • Make None type hints always explicit.
  • Use the "Annotated Field" method of instantiating defaults on Fields for submodels.
• Change base_url to a computed_field so it can be serialized. It's possible this should be done in additional places or that other models should have their calculated property fields excluded from serialization.

[github-actions]

Test Results

246 tests   244 ✅  55s ⏱️
  1 suites    2 💤
  1 files      0 ❌

Results for commit 5f8569b.

[bschwedler]

Thank you for doing this!