Emit a warning when instrumentation encounters a type it cannot check

[agronholm]

Things to check first

• I have searched the existing issues and didn't find my feature already requested there

Feature description

The instrumentation code should emit an InstrumentationWarning (when in debug mode) when it encounters a type that has been designated as "ignored" (due to, for example, being imported under if TYPE_CHECKING:.

Use case

It may be sometimes difficult to understand why a type check has been omitted from the instrumented code. Adding code comments for this is not possible because comments are not part of the abstract syntax tree.

[agronholm]

There is the option of storing the comments on the transformer itself, and injecting them into the debug output using less sophisticated methods like string searching. This is very difficult to do reliably though.