chore: replace pydantic models with stdlib dataclasses

[tylerjroach]

Summary

• replace Pydantic feature-flag models with standard-library dataclasses and lenient from_dict parsers
• remove the Pydantic dependency and update uv.lock
• fix OpenFeature configuration examples and update repository guidance

Closes #190.

Testing

• ruff format --check .
• ruff check .
• pytest --cov --cov-branch --cov-report=term-missing (387 passed)
• pytest --cov --cov-branch --cov-report=term-missing openfeature-provider/tests/ (52 passed)
• uv lock --check

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The new parsers preserve required nested feature-flag construction, ignore forward-compatible extra fields, and the provider call sites consistently use the replacement dataclass APIs.

Important Files Changed

Filename	Overview
mixpanel/flags/types.py	Replaces Pydantic DTOs with dataclasses and explicit parsers while preserving nested model construction and fallback-copy behavior.
mixpanel/flags/local_feature_flags.py	Switches local definitions to dataclass parsing and uses deepcopy when applying rollout-specific variant splits.
mixpanel/flags/remote_feature_flags.py	Switches remote flag responses from Pydantic validation to the new parser.
pyproject.toml	Removes the Pydantic runtime dependency and updates related lint guidance.
uv.lock	Removes Pydantic and its transitive packages without changing the investigated advisory-bearing dependencies.

_{Reviews (1): Last reviewed commit: "chore: replace pydantic models with stdl..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.39%. Comparing base (a4f669a) to head (8d1c84a).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
+ Coverage   96.33%   96.39%   +0.06%     
==========================================
  Files          15       15              
  Lines        2838     2888      +50     
  Branches      176      176              
==========================================
+ Hits         2734     2784      +50     
  Misses         67       67              
  Partials       37       37              

Flag	Coverage Δ
openfeature-provider	51.24% <72.05%> (+0.52%)	⬆️

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