fix various Match statement visitation errors

[zsol]

fix various Match statement visitation errors

Fixes #1160.

This PR also

• fixes whitespace_before_colon being swallowed during visitation on MatchCases
• adds a new type of roundtrip test that catches issues of this class: the test applies a noop transformer to exercise the visitation API and compares the result with the original source.
• adds a few more cases to the match fixture

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.26%. Comparing base (9f6e276) to head (e259e18).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1161 +/- ## ========================================== + Coverage 91.15% 91.26% +0.10% ========================================== Files 261 261 Lines 26864 26877 +13 ========================================== + Hits 24489 24529 +40 + Misses 2375 2348 -27 ```

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