Add ChatCompletionCache along with AbstractStore for caching completions #3526

Job	Run time
format	18s
lint	26s
mypy (./packages/autogen-core)	18s
pyright (./packages/autogen-core)	17s
mypy (./packages/autogen-magentic-one)	16s
pyright (./packages/autogen-magentic-one)	17s
mypy (./packages/agbench)	25s
pyright (./packages/agbench)	17s
mypy (./packages/autogen-ext)	24s
pyright (./packages/autogen-ext)	15s
mypy (./packages/autogen-agentchat)	18s
pyright (./packages/autogen-agentchat)	18s
check-proto-changes-python	42s
mypy (./packages/magentic-one-cli)	16s
pyright (./packages/magentic-one-cli)	27s
codecov (./packages/autogen-core)	25s
codecov (./packages/autogen-magentic-one)	19s
docs (./packages/autogen-core)	19s
docs-example-check (./packages/autogen-core)	17s
codecov (./packages/autogen-ext)	27s
codecov (./packages/autogen-agentchat)	17s
markdown-code-lint	17s
samples-code-check	20s
test (./packages/autogen-core)	18s
test (./packages/autogen-magentic-one)	17s
test (./packages/autogen-ext)	15s
test (./packages/autogen-agentchat)	18s
	9m 3s

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