fix(catalog): apply a MemTable DELETE or UPDATE when the plan runs

[michaelsembwever]

Which issue does this PR close?

#24654

Rationale for this change

What changes are included in this PR?

EXPLAIN DELETE and EXPLAIN UPDATE changed the rows of a MemTable. handle_explain() builds the physical plan in order to print it, the physical planner calls the provider hook while it builds the plan, and MemTable did the whole row change inside the hook. The returned DmlResultExec was a constant node that only reported the count the hook had computed, so the plan text also carried the count.

Replace DmlResultExec with MemDmlExec. The hook now compiles the WHERE clause and the assignments, then returns a plan that holds the partitions and the declared sort order of the table. execute() applies the operation, clears the sort order, and emits the count. This is the pattern that the provider guide already recommends, and MemTable is the reference implementation.

Every check of the statement stays in the hook, so an EXPLAIN still reports an invalid statement. A plan that runs twice applies the operation twice, as DataSinkExec does for an INSERT.

The DmlResultExec: rows_affected=0 lines of delete.slt and update.slt become MemDmlExec: op=Delete and MemDmlExec: op=Update. The count is unknown while the plan is built, so it no longer appears in the plan text.

Are these changes tested?

Only with the tests here, which are based on the assumptions made in the issue.

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.89744% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.44%. Comparing base (a6e2d3f) to head (8e695f6).
⚠️ Report is 36 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/catalog/src/memory/table.rs	85.89%	10 Missing and 12 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24655      +/-   ##
==========================================
+ Coverage   81.36%   81.44%   +0.08%     
==========================================
  Files        1117     1118       +1     
  Lines      397872   399600    +1728     
  Branches   397872   399600    +1728     
==========================================
+ Hits       323725   325458    +1733     
+ Misses      55229    55137      -92     
- Partials    18918    19005      +87     

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