refactor(cli): extract shared epochs validation helper

[nk-pavan-official]

Summary

This PR refactors the CLI handling for --epochs by extracting the duplicated ConfigError handling into a shared helper. It also simplifies the error message for invalid epoch values while preserving task attribution in the eval-set path.

Changes

• Added _apply_epochs_or_exit() next to _resolve_or_exit()
• Moved replace(task, epochs=...) and ConfigError handling into the shared helper
• Removed duplicated try/except blocks from _cmd_run and _cmd_eval_set
• Moved the Task import under TYPE_CHECKING
• Simplified the error message to --epochs must be >= 1, got N
• Preserved task attribution for the eval-set path (--epochs must be >= 1, got N (task 'NAME'))
• Updated the CLI tests to use exact pytest.raises(..., match=...) assertions
• Updated CHANGELOG.md under the Unreleased section

Checklist

• pre-commit install done; hooks pass (or ran pre-commit run --all-files)
• Tests added/updated
• Coverage stays at 100% (pytest --cov)
• ruff check . and ruff format --check . pass
• mypy passes (strict)
• CHANGELOG.md updated under "Unreleased"
• No public API changes
• Core stays NumPy-only (no new dependencies)

Related

Closes #152