feat: save/load test for dotnet agents #4386

Job	Run time
check-proto-changes-python	1m 23s
docs (./packages/autogen-core)	1m 50s
docs-example-check (./packages/autogen-core)	3m 14s
format	55s
lint	58s
markdown-code-lint	2m 32s
mypy (./packages/autogen-core)	3m 50s
mypy (./packages/agbench)	1m 8s
mypy (./packages/autogen-ext)	3m 4s
pyright (./packages/autogen-core)	1m 10s
samples-code-check	59s
mypy (./packages/autogen-agentchat)	1m 35s
pyright (./packages/agbench)	1m 9s
pyright (./packages/autogen-ext)	1m 17s
test (./packages/autogen-core)	1m 4s
mypy (./packages/magentic-one-cli)	1m 25s
test (./packages/autogen-ext)	4m 49s
pyright (./packages/autogen-agentchat)	57s
test (./packages/autogen-agentchat)	1m 18s
pyright (./packages/magentic-one-cli)	59s
codecov (./packages/autogen-core)	13s
codecov (./packages/autogen-ext)	8s
codecov (./packages/autogen-agentchat)	13s
	36m 10s

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