Add custom agent reasoning effort across SDKs #3066

Job	Run time
.NET SDK Tests (ubuntu-latest, inprocess)	7m 59s
.NET SDK Tests (macos-latest, default)	5m 27s
.NET SDK Tests (windows-latest, default)	21m 37s
.NET SDK Tests (macos-latest, inprocess)	10m 32s
.NET SDK Tests (ubuntu-latest, default)	9m 10s
	54m 45s

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