poly check: ignore dependencies within TYPE_CHECKING statement 🎉

[DavidVujic]

From version 1.40 of the CLI and 1.46 of the Poetry plugin, the poly tool will ignore any imports (bricks or third-party) that are defined within an:

from typing import TYPE_CHECKING


if TYPE_CHECKING:
   # import statements that are only used in dev and should be ignored by the poly commands

This means that the poly check command will not report on missing dependencies for imports that are defined within the typing.TYPE_CHECKING clause. This is useful for imported modules that only contain types used for typing annotations and not during runtime. Tools like MyPy already respects this syntax.

There's one limitation though:
The poly commands (check, libs and test diff) will locate imports to ignore that are directly within the if clause, but not if there is nesting - such as a function definition within the if TYPE_CHECKING statement, that has imports in the function body.

The idea origins from issue #336 and is requested by several Polylith users ⭐

Implementation details in Pull Request #406