Handle object as Any, and support subscripted generic protocols and TypedDicts

[mauvilsa]

What does this PR do?

Extends the type hint support for generics and unifies the handling of object
with Any.

Added

• Support for a subscripted generic TypedDict, e.g. SomeDict[int], and for a TypedDict that inherits from one, e.g. class SubDict(SomeDict[int]), both previously unsupported. Subscripting doesn't change which keys are accepted, only the types of the keys annotated with a TypeVar, composing the substitutions along the inheritance chain. Works for parsing, the --*.help option and shtab completions.
• A TypeVar default, constraint or bound given as a forward reference is now resolved with the names of the module in which the TypeVar is defined. An unresolvable reference becomes an Unvalidated<...> instead of failing.
• Keys of a TypedDict whose type can't be validated now accept any value, the same as signature parameters already did.

Fixed

• A subscripted generic Protocol, e.g. Proto[int], never being implementable. The type arguments are now substituted into the protocol's method signatures and return types, so Proto[int] and Proto[str] accept different implementations, and a TypeVar that remains matches any type, as static type checkers do. This also applies to instance factory protocols, i.e. the return type of a subscripted protocol's __call__.
• Internal RuntimeError when giving a value for a TypedDict key annotated with a TypeVar.
• type[Any] rejecting every value, instead of accepting any class as bare type does.
• The docstring of a subscripted generic class not being used, so the group description and the parameter descriptions were missing in the help.
• Nested namespaces in init_args, e.g. a subclass spec kept as is for an Any typed parameter, being expanded into keyword arguments on instantiate.

Changed

• object as a type is now handled exactly like Any, since in standard typing every value is an instance of it. This means it no longer only accepts the import path of a class, it accepts any value, it participates in the validate_subclass_spec_in_any and instantiate_subclass_spec_in_any settings, it is sorted last in unions together with Any and Unvalidated<...>, and dumping it warns about values that lose their type.

Before submitting

• Did you read the contributing guideline?
• If you used a coding agent, did you fully understand and validate all generated code and ensure it follows the contributing guidelines?
• Did you update the documentation? (readme and public docstrings)
• Did you write unit tests such that there is 100% coverage on related code? (required for bug fixes and new features)
• Did you verify that new and existing tests pass locally?
• If this is a bug fix, did you verify that the tests fail without the code fix?
• Did you make sure that all changes preserve backward compatibility?
• Did you update the CHANGELOG including a pull request link? (not for typos, docs, test updates, or minor internal changes/refactors)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (31f19f5) to head (3bd255a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #958   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           27        27           
  Lines         8600      8671   +71     
=========================================
+ Hits          8600      8671   +71     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
7 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud