Add proper detection of test-only modules using TEST_MODULES registry

[GKotsifos]

Fixes Error message on using test vendors out of test scope #120

Description of changes in release / Impact of release:

Adds proper detection of test-only modules (unittest, asserts). When these modules are imported outside test mode, Larky now throws a clear and informative error instead of a generic exception.

Documentation

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Risks of this release

Is this a breaking change?

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• No

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Is there a way to disable the change?

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[mahmoudimus]

Hmm your pull request description says, "throws a clear and informative error instead of a generic exception" -- is there a generic exception being thrown right now? What test do we have that can confirm this? What test do we have that can confirm the scenario where this exception is thrown as well?

[GKotsifos]

Hmm your pull request description says, "throws a clear and informative error instead of a generic exception" -- is there a generic exception being thrown right now? What test do we have that can confirm this? What test do we have that can confirm the scenario where this exception is thrown as well?

I want to make sure I fully understand what you are asking for. We already have .star tests that import unittest and asserts. Are you looking for new Junit test that explicitly loads a test-only module in a non-test context and asserts on the exact error message or something else?