feat: save/load test for dotnet agents #4384

Job	Run time
format	51s
lint	53s
docs (./packages/autogen-core)	1m 39s
docs-example-check (./packages/autogen-core)	3m 9s
mypy (./packages/autogen-core)	3m 38s
pyright (./packages/autogen-core)	58s
mypy (./packages/agbench)	1m 8s
samples-code-check	59s
pyright (./packages/agbench)	55s
mypy (./packages/autogen-ext)	3m 9s
pyright (./packages/autogen-ext)	1m 19s
test (./packages/autogen-core)	1m 1s
mypy (./packages/autogen-agentchat)	1m 30s
pyright (./packages/autogen-agentchat)	1m 0s
test (./packages/autogen-ext)	4m 32s
mypy (./packages/magentic-one-cli)	1m 25s
pyright (./packages/magentic-one-cli)	1m 0s
test (./packages/autogen-agentchat)	1m 1s
check-proto-changes-python	1m 10s
markdown-code-lint	2m 35s
codecov (./packages/autogen-core)	8s
codecov (./packages/autogen-ext)	9s
codecov (./packages/autogen-agentchat)	9s
	34m 18s

Provide feedback