Fix projection for fluent union list fields

[michaelstaib]

Summary

• fix QueryableProjectionScopeExtensions.CreateSelection to project list/array/set items using the target member element type instead of always using scope runtime type
• this prevents Expression.Bind type mismatches for fluent UnionType list fields where the union runtime type defaults to object
• add regression test reproducing List of union type inside object type causes an exception when using fluent API #5528 with UseProjection over a list field configured as a fluent union

Validation

• dotnet test src/HotChocolate/Data/test/Data.Tests/ --filter FullyQualifiedName~Issue5528ReproTests.List_Of_Union_With_Fluent_Api_And_Projection_Does_Not_Throw -f net10.0
• dotnet test src/HotChocolate/Data/test/Data.Tests/ --filter FullyQualifiedName~QueryContextUnionProjectionTests -f net10.0
• dotnet test src/HotChocolate/Data/test/Data.Projections.Tests/ -f net10.0

Fixes #5528

[github-actions]

Fusion Gateway Performance Results

Simple Composite Query

	Req/s	Err%
Constant 2 (50 VUs)	3135.58	0.00%
Ramping 2 (0-500-0 VUs)	3768.68	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	1.21ms	12.73ms	15.64ms	25.75ms	35.75ms	262.48ms
Ramping 2	1.27ms	52.67ms	58.15ms	100.66ms	144.32ms	287.19ms

---

Deep Recursion Query

	Req/s	Err%
Constant 2 (50 VUs)	742.99	0.00%
Ramping 2 (0-500-0 VUs)	883.05	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	6.96ms	58.08ms	65.03ms	82.46ms	100.53ms	734.03ms
Ramping 2	3.18ms	210.47ms	233.54ms	488.07ms	547.96ms	868.16ms

---

Variable Batching Throughput

	Req/s	Err%
Constant 2 (50 VUs)	5734.12	0.00%
Ramping 2 (0-500-0 VUs)	5229.55	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	0.15ms	8.15ms	8.62ms	14.45ms	17.32ms	82.08ms
Ramping 2	0.18ms	39.78ms	43.92ms	81.76ms	105.16ms	233.73ms

---

Runner 2 = benchmarking-2

Run 22421092140 • Commit 50d3b77 • Thu, 26 Feb 2026 00:03:08 GMT

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (f64f691) to head (a83c12e).

Additional details and impacted files

@@     Coverage Diff      @@
##   main   #9222   +/-   ##
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