Add IDE type narrowing to generated validator mixins

[alganet]

Part of a PR group: Fluent - FluentGen - Validation

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Make validator chains narrow types for IDEs and PHPStan without the FluentAnalysis extension, driven entirely by the generated src/Mixins PHPDoc.

• Annotate src/Validators with #[Assurance] / #[AssuranceSubject] declaring each rule's assured type.
• Regenerate src/Mixins: Chain becomes generic (@template-covariant TSure); static entry methods narrow to Chain; assert()/check() carry an unconditional @phpstan-assert TSure. Container rules (key/property/length/ max/min) and the concrete prefix forms (nullOrIntType, keyIntType, allIntType) narrow; argument-wrapping and compose forms stay Chain so a raw (non-fluent) Validator argument is still accepted.
• isValid() intentionally does not narrow: its only conditional form is a two-way guard, unsound for inexact rules on the false branch.
• Add the tests/inference static-narrowing suite (no extension config) and run it in CI; scope the phpstan/phpcs accommodations for generated mixins.

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This PR group adds advanced static (no PHPStan extension needed) type support and narrowing for fluent chains, pioneering it for Validation (StringFormatter should also be compatible with this approach)

In the example above, the devsense extension for VSCode is correctly infering an int[] (iterable int) from a each(int()) fluent validation chain.

More examples in tests/inference/assertions/static-narrowing.php.

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Notes:

• Most of the big diff is generated mixins, the PR is actually small.
• This work is related, but distinct from Integrate Fluent, FluentGen and FluentAnalysis #1730. FluentAnalysis offers dynamic type narrowing with much richer narrowings (but IDEs can't run the extension). This one offers basic, static narrowing for IDEs such as devsense (tested) and IntelliJ (untested).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.14%. Comparing base (639f02f) to head (3d288ea).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1802   +/-   ##
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  Coverage     97.14%   97.14%           
  Complexity     1096     1096           
=========================================
  Files           198      198           
  Lines          2554     2554           
=========================================
  Hits           2481     2481           
  Misses           73       73           

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[alganet]

@henriquemoody these are in draft because of the branch-alias (we need to amend the real composer versions when we do the release dance).

However, although not packagist-ready yet, they are open for review of the code. I requested review only here to avoid spam but you're free to comment in any of the 3.

[henriquemoody]

This is trully trully awesome!!

[alganet]

I have removed the #[Assurance attributes that are not relevant for this PR, keeping only the ones that actively contribute to the IDE-only static narrowing. The ones removed belong to the full FluentAnalysis phpstan-extension integration that doesn't really affect IDE behavior.

Hopefully, this would make clear what IDEs can do and what they cannot (the static-narrowing.php file is a good reference card though, and remains the same).

[henriquemoody]

This is absolutely amazing! I'm so happy you got this one working, it really puts Validation on the next level!