Add ChatCompletionCache along with AbstractStore for caching completions #3571

Job	Run time
codecov (./packages/autogen-core)	1m 2s
format	59s
lint	1m 0s
codecov (./packages/autogen-magentic-one)	3m 24s
codecov (./packages/autogen-ext)	49m 43s
mypy (./packages/autogen-core)	2m 29s
codecov (./packages/autogen-agentchat)	1m 35s
mypy (./packages/autogen-magentic-one)	1m 19s
pyright (./packages/autogen-core)	54s
test (./packages/autogen-core)	1m 4s
mypy (./packages/agbench)	1m 6s
pyright (./packages/autogen-magentic-one)	56s
test (./packages/autogen-magentic-one)	1m 36s
mypy (./packages/autogen-ext)	2m 3s
pyright (./packages/agbench)	2m 7s
test (./packages/autogen-ext)	3m 7s
mypy (./packages/autogen-agentchat)	1m 34s
test (./packages/autogen-agentchat)	1m 10s
pyright (./packages/autogen-ext)	1m 12s
mypy (./packages/magentic-one-cli)	1m 22s
pyright (./packages/autogen-agentchat)	56s
pyright (./packages/magentic-one-cli)	52s
docs (./packages/autogen-core)	1m 34s
check-proto-changes-python	1m 18s
docs-example-check (./packages/autogen-core)	2m 52s
markdown-code-lint	2m 1s
samples-code-check	54s
	1h 30m 9s

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