[CHORE] Add support for pydantic v2

[HammadB]

Description of changes

Closes #893

Summarize the changes made by this PR.

• Improvements & Bug fixes
  • Adds support for pydantic v2.0 by changing how Collection model inits - this simple change fixes pydantic v2
  • Fixes the cross version tests to handle pydantic specifically
  • Conditionally imports pydantic-settings based on what is available. In v2 BaseSettings was moved to a new package.
• New functionality
  • N/A

Test plan

Existing tests were run with the following configs

1. Fastapi < 0.100, Pydantic >= 2.0 - Unsupported as the fastapi dependencies will not allow it. They likely should, as pydantic.v1 imports would support this, but this is a downstream issue.
2. Fastapi >= 0.100, Pydantic >= 2.0, Supported via normal imports ✅ (Tested with fastapi==0.103.1, pydantic==2.3.0)
3. Fastapi < 0.100 Pydantic < 2.0, Supported via normal imports ✅ (Tested with fastapi==0.95.2, pydantic==1.9.2)
4. Fastapi >= 0.100, Pydantic < 2.0, Supported via normal imports ✅ (Tested with latest fastapi, pydantic==1.9.2)

• Tests pass locally with pytest for python, yarn test for js

Documentation Changes

None required.

[github-actions]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readbility, Modularity, Intuitiveness)

[HammadB]

This fixes pydantic v2 because it needs attrs inited before it can assign to PrivateAttrs