[SYSTEMDS-3949] Extend Delta Spark round trip tests

[Jakob-al28]

The Spark round trip tests cover multi-file layouts, deletion vectors,
partitioning, column mapping and schema evolution. This adds three that were
missing: a log that has been checkpointed, a column type SystemDS cannot map,
and a table more than one engine has written to.

test	covers
checkpointBackedHistoryRead	a log that rolled into a parquet checkpoint, with a delete after it, so the snapshot comes from a checkpoint plus trailing commits
unsupportedColumnTypeRead	DATE / TIMESTAMP / DECIMAL columns, which have no SystemDS value type and must be rejected by name before decoding
systemdsCreateSparkAppendRead	SystemDS creates the table, Spark appends to it, so a mixed engine commit history still reads back as one table

[Baunsgaard]

LGTM, if it passes the CI tests we merge it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.45%. Comparing base (af500c8) to head (233edbe).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2580      +/-   ##
============================================
- Coverage     71.61%   71.45%   -0.16%     
- Complexity    50352    50409      +57     
============================================
  Files          1626     1629       +3     
  Lines        194664   195331     +667     
  Branches      38007    38078      +71     
============================================
+ Hits         139408   139574     +166     
- Misses        44328    44836     +508     
+ Partials      10928    10921       -7     

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