Add ChatCompletionCache along with AbstractStore for caching completions #3334

Job	Run time
check-proto-changes-python	1m 6s
codecov (./packages/autogen-core)	1m 0s
docs (./packages/autogen-core)	1m 27s
codecov (./packages/autogen-magentic-one)	1m 58s
docs-example-check (./packages/autogen-core)	2m 47s
format	58s
codecov (./packages/autogen-ext)	2m 39s
codecov (./packages/autogen-agentchat)	1m 11s
lint	58s
markdown-code-lint	2m 11s
mypy (./packages/autogen-core)	2m 18s
mypy (./packages/autogen-magentic-one)	1m 30s
pyright (./packages/autogen-core)	1m 0s
samples-code-check	1m 0s
mypy (./packages/agbench)	1m 4s
pyright (./packages/autogen-magentic-one)	1m 6s
test (./packages/autogen-core)	54s
mypy (./packages/autogen-ext)	1m 56s
pyright (./packages/agbench)	54s
test (./packages/autogen-magentic-one)	1m 22s
mypy (./packages/autogen-agentchat)	1m 22s
pyright (./packages/autogen-ext)	1m 2s
test (./packages/autogen-ext)	2m 59s
mypy (./packages/magentic-one-cli)	1m 18s
pyright (./packages/autogen-agentchat)	57s
test (./packages/autogen-agentchat)	1m 15s
pyright (./packages/magentic-one-cli)	1m 3s
	39m 15s

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