Fix dump round-tripping, generic protocols, TypeVar types and extend subclass spec validation

[mauvilsa]

What does this PR do?

Two related groups of changes.

Subclass spec validation beyond Any — the validate_subclass_spec_in_any setting now also applies to
Unvalidated<...> and to dicts that don't validate their values, e.g. dict[str, Any]. For dicts the spec is only
validated and the value kept as a dict, which matters for unions such as Union[SomeClass, dict[str, Any]], where a
spec rejected by the class member would otherwise be silently swallowed by the dict member.

Fixes around dumping and type resolution:

• dump and --print_config now round-trip values given as an import path to an instance. Previously the dump had a
  "not serializable" message unless the instance happened to be defined in the module of its class; now the import path
  the value was resolved from is remembered and dumped back.
• Parsing the secret mask ********** as a SecretStr (both jsonargparse's and pydantic's) now fails, instead of a
  config bootstrapped with --print_config silently making the mask the actual secret.
• A generic Protocol can now be implemented. Previously the TypeVar of the protocol and the type in the
  implementation could never be equal, so no class ever matched. A TypeVar on either side now matches any type, as
  static type checkers do.
• Classes whose __new__ is wrapped by a decorator, e.g. to mark them deprecated or experimental, no longer end up with
  no parameters at all. The parameters are resolved from __init__ instead of from the wrapper.
• A TypeVar used as the type itself, not only as the subtype of a type[...], is replaced by what it stands for: its
  PEP 696 default, its constraints or its bound. Previously the value was accepted without any validation.

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 (7a860bf) to head (8512e39).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #953   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           27        27           
  Lines         8305      8390   +85     
=========================================
+ Hits          8305      8390   +85     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
4 Accepted issues

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

See analysis details on SonarQube Cloud