Add ChatCompletionCache along with AbstractStore for caching completions #3538

Job	Run time
format	51s
lint	52s
mypy (./packages/autogen-core)	2m 28s
pyright (./packages/autogen-core)	1m 6s
mypy (./packages/autogen-magentic-one)	1m 14s
pyright (./packages/autogen-magentic-one)	1m 3s
mypy (./packages/agbench)	1m 4s
codecov (./packages/autogen-core)	1m 11s
mypy (./packages/autogen-ext)	2m 10s
pyright (./packages/agbench)	55s
codecov (./packages/autogen-magentic-one)	1m 58s
pyright (./packages/autogen-ext)	1m 9s
mypy (./packages/autogen-agentchat)	1m 24s
codecov (./packages/autogen-ext)	3m 22s
pyright (./packages/autogen-agentchat)	1m 11s
mypy (./packages/magentic-one-cli)	1m 22s
codecov (./packages/autogen-agentchat)	1m 18s
pyright (./packages/magentic-one-cli)	1m 4s
docs (./packages/autogen-core)	1m 28s
docs-example-check (./packages/autogen-core)	2m 46s
test (./packages/autogen-core)	1m 10s
test (./packages/autogen-magentic-one)	1m 42s
test (./packages/autogen-ext)	48m 1s
test (./packages/autogen-agentchat)	1m 12s
check-proto-changes-python	1m 19s
markdown-code-lint	2m 7s
samples-code-check	54s
	1h 26m 21s

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