fix: Partition aware source table UI widget swaps from merge to coalesce

[ericlln]

• Fixes the observed issue of the partition selector button flipping between Merge and Coalesce depending on which partition view is selected.
• The original condition for isPartitionAwareSourceTable in IrisGridTableModel.ts isn't always accurate as table.isUncoalesced is only true when no filters have been applied yet. Once a filter is applied, the table is no longer considered uncoalesced but the source table should still have the same property as before.
• Test snippet is linked on the ticket: DH-19015

[codecov]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 46.82%. Comparing base (99dfcab) to head (c607b70).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/iris-grid/src/IrisGridProxyModel.ts	0.00%	4 Missing ⚠️
packages/iris-grid/src/IrisGridTableModel.ts	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2397      +/-   ##
==========================================
- Coverage   46.82%   46.82%   -0.01%     
==========================================
  Files         711      711              
  Lines       39289    39295       +6     
  Branches    10007     9821     -186     
==========================================
+ Hits        18398    18400       +2     
- Misses      20837    20884      +47     
+ Partials       54       11      -43     

Flag	Coverage Δ
unit	46.82% <16.66%> (-0.01%)	⬇️

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