samples: add type hints to all samples

[anguillanneuf]

Add type hints so setting "enforce_type_hints" to True won't cause lint failures.

python-pubsub/samples/snippets/noxfile_config.py

Lines 26 to 28 in 2584147

	# Old samples are opted out of enforcing Python type hints
	# All new samples should feature them
	"enforce_type_hints": True,

[plamut]

@anguillanneuf What's the status of this, have you started working on type hints yet?

If not, I can probably handle this, I'll have some spare cycles.

[anguillanneuf]

@plamut Thanks for the ping. If you can handle it, I will review. Thanks again!