Add custom agent reasoning effort across SDKs #3067

Job	Run time
.NET SDK Tests (macos-latest, default)	9m 33s
.NET SDK Tests (macos-latest, inprocess)	9m 13s
.NET SDK Tests (ubuntu-latest, inprocess)	8m 32s
.NET SDK Tests (windows-latest, default)	22m 24s
.NET SDK Tests (ubuntu-latest, default)	9m 35s
	59m 17s

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