Add custom agent reasoning effort across SDKs #3065

Job	Run time
.NET SDK Tests (windows-latest, default)	20m 32s
.NET SDK Tests (ubuntu-latest, inprocess)	7m 32s
.NET SDK Tests (macos-latest, default)	8m 58s
.NET SDK Tests (macos-latest, inprocess)	9m 25s
.NET SDK Tests (ubuntu-latest, default)	9m 13s
	55m 40s

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