Report impure methods overriding @pure-unless-parameter-passed methods

[zonuexe]

Follow-up to #6018. A method marked @pure-unless-parameter-passed tells callers it is pure as long as the flagged out parameter is omitted, but an override marked @phpstan-impure can break that without any error. @pure-unless-callable-is-impure already has this check (method.impureOverridePureUnlessCallable); this adds the same for the new tag.

Changes

• MethodSignatureRule reports Impure method %s::%s() overrides method %s::%s() marked @pure-unless-parameter-passed. with the identifier method.impureOverridePureUnlessParameterPassed.
• Like the existing check, it only runs with reportMethodPurityOverride (bleeding edge) and only for an override that is explicitly impure; an override without a purity tag or one marked @phpstan-pure is not reported.
• When the parent carries both tags, only the @pure-unless-callable-is-impure error is reported, so each parent method still yields at most one error.

Not in this PR: the signature checks in FunctionPurityCheck (e.g. a non-optional parameter marked @pure-unless-parameter-passed) only run for methods with a body, so interface and abstract methods aren't checked. That applies to the existing @phpstan-pure checks as well, so I'd handle it separately.

[staabm]

Please add another test with @phpstan-all-methods-pure

[zonuexe]

I added this in 6fa0be6. PHPStan reports an implementation in a @phpstan-all-methods-impure class the same way as one marked @phpstan-impure, and leaves one in a @phpstan-all-methods-pure class alone.

I left out the other direction, a @phpstan-all-methods-pure class that declares the @pure-unless-parameter-passed method itself, because PHPStan gets that case wrong: it lets the class-level tag override the method's own tag and treats the method as unconditionally pure. It then misses a caller that passes $count, and reports an impure override as method.impure ("overrides pure method") instead of the new error. @pure-unless-callable-is-impure on 2.3.x has the same problem: in such a class, PHPStan misses an impure callback too. I'll fix both tags in a separate PR.

[staabm]

Thank you