test(integration): add GroupBy + Count composition test over search filter

[daniel3303]

Summary

• Adds the first integration test that runs GroupBy(...).Select(g => new { g.Key, Count = g.Count() }) over a EF.Functions.Matches filter. The SQL shape (search predicate in WHERE + GROUP BY + aggregate) is the one behind any "hits per facet" UI.
• A regression in ParadeDbQuerySqlGenerator that mishandles aggregate composition (e.g., search predicate pushed past the GROUP BY, or score function leaking into the aggregate scope) would slip past the existing single-row Where/Select tests.

Code changes

• Equibles.ParadeDB.EntityFrameworkCore.IntegrationTests/SearchWithGroupByCountTests.cs — new [Fact] filtering articles by Matches(content, "models OR pasta"), grouping by Category, projecting (Category, Count()), and asserting machine-learning=2, cooking=1, and physics absent.

Test plan

• dotnet test --filter "FullyQualifiedName~SearchWithGroupByCountTests" --framework net10.0 passes locally against a paradedb/paradedb:latest Testcontainer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.56%. Comparing base (20cbb3f) to head (c76ad1b).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #98   +/-   ##
=======================================
  Coverage   99.56%   99.56%           
=======================================
  Files          25       25           
  Lines        1157     1157           
  Branches      128      128           
=======================================
  Hits         1152     1152           
  Misses          1        1           
  Partials        4        4           

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