[ty] Check typeshed VERSIONS for parent modules when reporting failed stdlib imports

[Gankra]

This is a drive-by improvement that I stumbled backwards into while looking into

• distinguish "doesn't exist" from "doesn't exist on this Python version" ty#296

I was writing some simple tests for "thing not in old version of stdlib" diagnostics and checked what was added in 3.14, and saw compression.zstd and to my surprise discovered that import compression.zstd and from compression import zstd had completely different quality diagnostics.

This is because compression and compression.zstd were both introduced in 3.14, and so per VERSIONS policy only an entry for compression was added, and so we don't actually have any definite info on compression.zstd and give up on producing a diagnostic. However the from compression import zstd form fails on looking up compression and we do have an exact match for that, so it gets a better diagnostic!

(aside: I have now learned about the VERSIONS format and I really wish they would just enumerate all the submodules but, oh well!)

The fix is, when handling an import failure, if we fail to find an exact match we requery with the parent module. In cases like compression.zstd this lets us at least identify that, hey, not even compression exists, and luckily that fixes the whole issue. In cases where the parent module and submodule were introduced at different times then we may discover that the parent module is in-range and that's fine, we don't produce the richer stdlib diagnostic.

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

scikit-build-core (https://github.com/scikit-build/scikit-build-core)
- src/scikit_build_core/build/_wheelfile.py:51:22: error[no-matching-overload] No overload of function `field` matches arguments
- Found 52 diagnostics
+ Found 51 diagnostics

No memory usage changes detected ✅

[Gankra]

(Broken into two commits so you can see the before and after on the snapshot)

[Gankra]

Can't help but wonder if we could statically precompute a Complete VERSIONS map...

[AlexWaygood]

Ahh thank you!!

[AlexWaygood]

Ah nice -- can you move these existing tests to this file so that all our tests for this feature are in the same place?

ruff/crates/ty_python_semantic/resources/mdtest/import/basic.md

Lines 180 to 207 in 5fb1423

	## Attempting to import a stdlib module that's not yet been added
	<!-- snapshot-diagnostics -->
	```toml
	[environment]
	python-version = "3.10"
	```
	```py
	import tomllib # error: [unresolved-import]
	from string.templatelib import Template # error: [unresolved-import]
	from importlib.resources import abc # error: [unresolved-import]
	```
	## Attempting to import a stdlib module that was previously removed
	<!-- snapshot-diagnostics -->
	```toml
	[environment]
	python-version = "3.13"
	```
	```py
	import aifc # error: [unresolved-import]
	from distutils import sysconfig # error: [unresolved-import]
	```

[Gankra]

I did this but I completely misread the direction you wanted this to go so instead my new test file is deleted and I added a new test to basic.md

[AlexWaygood]

Haha, I don't mind either way, I'd just like all the tests for the feature to be together!