fix: specify parameter names in Model @phpstan-method callable types

[gr8man]

Description

Fixes PhpStorm docblock parsing errors (Expected: variable) on Model @phpstan-method annotations for when() and whenNot() methods by:

1. Adding explicit mixed type hint to $condition parameter (mixed $condition).
2. Specifying parameter names $builder and $value in the callable(...) signature.
3. Replacing (callable(...))|null with standard nullable type syntax ?callable(...).

Fixes #10443

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

This is still red on PHPStorm.

[paulbalandan]

And pls use the PR template moving forward.