adds integration test for the InMemoryRuntime #2333

Job	Run time
format	52s
mypy (./packages/autogen-core)	1m 57s
lint	57s
mypy (./packages/autogen-magentic-one)	1m 15s
mypy (./packages/agbench)	52s
check-proto-changes-python	1m 7s
docs (./packages/autogen-core)	1m 31s
mypy (./packages/autogen-ext)	1m 43s
docs-example-check (./packages/autogen-core)	2m 3s
mypy (./packages/autogen-agentchat)	1m 2s
pyright (./packages/autogen-core)	57s
test (./packages/autogen-core)	52s
pyright (./packages/autogen-magentic-one)	57s
test (./packages/autogen-magentic-one)	1m 23s
pyright (./packages/agbench)	53s
test (./packages/autogen-ext)	2m 10s
pyright (./packages/autogen-ext)	58s
test (./packages/autogen-agentchat)	58s
pyright (./packages/autogen-agentchat)	1m 2s
	23m 29s

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