Extend simulation infrastructure with Now()

[lekcyjna123]

In some places it is useful to have direct access to the current cycle number. Till now we could manually count cycles, but this required using call_try everywhere. This commit ports simulation framework extension from #395. There is added new class Now() which can be yielded during testing. In return a current cycle will be returned.

This feature is needed to extend and port CondVar from #395

coreblocks/test/common.py

Lines 429 to 433 in ddb21b5

	class CondVar:
	"""
	Simple CondVar. It has some limitations e.g. it can not notify other process
	without waiting a cycle.
	"""

Current CondVar notification requires to wait a cycle on notify. With usage of Now() it should be possible to omit this waiting.

[Kristopher38]

LGTM, left one non-critical question

[Kristopher38]

Could you elaborate why this needs to be conditioned on typechecking?

[lekcyjna123]

Because in infrastructure.py file I import symbols from functions.py. So without this if there is a circular dependency.

[tilk]

Let's finally merge some testing extensions.