test: cover partitionValues_parsed in partitioned write tests

[scottsand-db]

What changes are proposed in this pull request?

Update test_write_partitioned_normal_values_roundtrip and test_write_partitioned_null_values_roundtrip in write_partitioned.rs to also cross-test writing parsed partition values (on/off)

How was this change tested?

cargo nextest run -p delta_kernel --test write_partitioned --all-features — 90 cases pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.40%. Comparing base (6486bd2) to head (1b9f4b9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2467   +/-   ##
=======================================
  Coverage   88.40%   88.40%           
=======================================
  Files         178      178           
  Lines       58235    58235           
  Branches    58235    58235           
=======================================
  Hits        51485    51485           
  Misses       4783     4783           
  Partials     1967     1967           

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