Clean up CI/CD workflow cache configuration and remove deprecated commands

[Copilot]

Addresses two CI/CD workflow inefficiencies identified in review comments on PR #7:

Cache configuration cleanup

• Removed duplicate restore-keys entry that redundantly matched the primary cache key with a trailing dash
• Keeps only the GHC version prefix fallback for broader cache reuse

Removed deprecated cabal command

• Eliminated cabal v2-update call since cabal update already handles source-repository-packages
• The v2- prefix is deprecated in modern Cabal versions

# Before: redundant cache fallback
restore-keys: |
  ${{ runner.os }}-cabal-${{ matrix.ghc-version }}-${{ hashFiles(...) }}-
  ${{ runner.os }}-cabal-${{ matrix.ghc-version }}-

# After: single meaningful fallback
restore-keys: |
  ${{ runner.os }}-cabal-${{ matrix.ghc-version }}-

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Note

Streamlines the GitHub Actions workflow in /.github/workflows/build-and-test.yml.

• Simplifies Cabal store caching by removing the redundant restore-keys entry; keeps only the GHC-version prefix fallback
• Removes deprecated cabal v2-update; retains cabal update for source updates
• No changes to build/test commands or matrix config beyond these cleanups

^{Written by Cursor Bugbot for commit 6909c99. This will update automatically on new commits. Configure here.}