Fix projection to preserve EF constructor-injected services

[michaelstaib]

• preserve existing projected instances for types that expose non-public parameterized constructors
• keep the projection pipeline from reconstructing those types with new T { ... }, which drops EF constructor-injected services
• add an EF regression test covering [UseProjection] with constructor-injected DbContext behavior

Closes #5449

[github-actions]

Fusion Gateway Performance Results

Simple Composite Query

	Req/s	Err%
Constant 2 (50 VUs)	3250.79	0.00%
Ramping 2 (0-500-0 VUs)	3834.90	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	1.13ms	12.44ms	15.11ms	24.25ms	33.59ms	252.45ms
Ramping 2	1.10ms	52.50ms	57.04ms	99.11ms	142.67ms	283.26ms

---

Deep Recursion Query

	Req/s	Err%
Constant 2 (50 VUs)	650.08	0.00%
Ramping 2 (0-500-0 VUs)	789.27	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	11.07ms	66.58ms	74.00ms	94.70ms	118.49ms	818.22ms
Ramping 2	2.91ms	235.60ms	261.40ms	546.37ms	610.39ms	1049.35ms

---

Variable Batching Throughput

	Req/s	Err%
Constant 2 (50 VUs)	6052.70	0.00%
Ramping 2 (0-500-0 VUs)	6390.74	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	0.15ms	7.73ms	8.16ms	13.49ms	16.59ms	56.27ms
Ramping 2	0.14ms	31.35ms	35.95ms	66.13ms	92.87ms	202.50ms

---

Runner 2 = benchmarking-2

Run 22417123165 • Commit 134ad9c • Wed, 25 Feb 2026 22:39:00 GMT