Added new error message and test for dict[str, Any] generation

[LachlanJW]

v0.3.3 added native dict generation, which is great, but silently breaks when the dict value type is unresolvable by assertical (e.g. Any, Path, object). Instead of a clear error, generation crashes deep in the stack:

Exception: Type None does not inherit from one of dict_keys([...])

This is because enumerate_class_properties sets second_type_to_generate = None when the value type can't be resolved, but generate_class_instance then passes None to generate_member, which calls generate_class_instance(None, ...) causing the crash.

This was already handled cleanly by keys:

if member.type_to_generate is None:
if not (optional_is_none and member.is_optional):
raise Exception(f"...cannot be generated")

Now added the error message to values to make it a little easier to trace.

The reason why I think this is useful is from a cryptic issue I found after this upgrade in another repo. When generating a dict[str, Any] prior to assertical v0.3.3, the assertical_extensions fixture registered register_value_generator(dict, lambda _: {}), which intercepted any dict field and returned {} before assertical inspected the type arguments. This masked the fact that Any is not a type assertical can generate. Now these are no longer intercepted and fail with the error described above. This new message would have made things easier!

[github-actions]

✅ Code coverage on dict_value_error_message is at 91% (compared to main being at 91%)

🎉 No files have reduced coverage 🎉

Full Coverage Report

File	Details
src/assertical/__init__.py	✅ 100% → 100%
src/assertical/asserts/__init__.py	✅ 100% → 100%
src/assertical/asserts/generator.py	✅ 100% → 100%
src/assertical/asserts/pandas.py	✅ 88% → 88%
src/assertical/asserts/time.py	✅ 95% → 95%
src/assertical/asserts/type.py	✅ 92% → 92%
src/assertical/fake/__init__.py	✅ 100% → 100%
src/assertical/fake/asyncio.py	✅ 100% → 100%
src/assertical/fake/generator.py	✅ 94% → 94%
src/assertical/fake/http.py	✅ 71% → 71%
src/assertical/fixtures/__init__.py	✅ 100% → 100%
src/assertical/fixtures/environment.py	✅ 100% → 100%
src/assertical/fixtures/fastapi.py	✅ 97% → 97%
src/assertical/fixtures/generator.py	✅ 100% → 100%
src/assertical/snapshot.py	✅ 100% → 100%
TOTAL	✅ 91% → 91%