Add Model Client Cache section to migration guide (#5197) #3857

Job	Run time
mypy (./packages/autogen-core)	3m 34s
mypy (./packages/autogen-magentic-one)	1m 20s
mypy (./packages/agbench)	1m 5s
docs (./packages/autogen-core)	1m 39s
mypy (./packages/autogen-ext)	2m 51s
docs-example-check (./packages/autogen-core)	3m 0s
mypy (./packages/autogen-agentchat)	1m 24s
mypy (./packages/magentic-one-cli)	1m 25s
format	55s
lint	52s
markdown-code-lint	2m 6s
pyright (./packages/autogen-core)	1m 7s
pyright (./packages/autogen-magentic-one)	1m 3s
samples-code-check	1m 0s
pyright (./packages/agbench)	1m 3s
test (./packages/autogen-core)	1m 12s
pyright (./packages/autogen-ext)	1m 8s
test (./packages/autogen-magentic-one)	1m 51s
pyright (./packages/autogen-agentchat)	1m 10s
test (./packages/autogen-ext)	4m 24s
pyright (./packages/magentic-one-cli)	55s
test (./packages/autogen-agentchat)	1m 4s
check-proto-changes-python	1m 24s
codecov (./packages/autogen-core)	12s
codecov (./packages/autogen-magentic-one)	9s
codecov (./packages/autogen-ext)	8s
codecov (./packages/autogen-agentchat)	7s
	38m 8s

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