chore: remove redundant CI steps

[itsoyou]

SYN-66
SYN-75

[cursor]

PR Summary

Low Risk
Workflow-only change; no application code or runtime behavior is affected, with only a small chance that Hatch and the removed action differed on Ruff target-version settings.

Overview
Removes the standalone Prepare lint / Lint steps from .github/workflows/tests.yml so CI no longer runs chartboost/ruff-action with a per-matrix PYTHON_TARGET.

Linting stays covered by the existing Type checking and Formatting step (hatch fmt --check), which already runs ruff (plus formatting and mypy) per project docs.

^{Reviewed by Cursor Bugbot for commit 269080d. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.47%. Comparing base (c9567ac) to head (269080d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   93.47%   93.47%           
=======================================
  Files          10       10           
  Lines         904      904           
  Branches      135      135           
=======================================
  Hits          845      845           
  Misses         34       34           
  Partials       25       25           

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