Report a docblock that combines a purity tag with a @pure-unless-* tag

[zonuexe]

Follow-up to #6669, which leaves this case out. A docblock that marks a function or method @phpstan-pure or @phpstan-impure and also makes its purity conditional with @pure-unless-callable-is-impure or @pure-unless-parameter-passed contradicts itself, and PHPStan follows a different tag depending on where it looks:

/**
 * @param callable(string): string $cb
 * @phpstan-impure
 * @pure-unless-callable-is-impure $cb
 */
function map(callable $cb, string $subject): string
{
	echo $subject; // Impure echo in pure function map().

	return $cb($subject);
}

With @phpstan-impure, callers see an impure function, since SimpleImpurePoint::createFromVariant() skips the conditional verdict once isPure() is no, while FunctionPurityCheck checks the body against the conditional tag and reports the echo.

With @phpstan-pure, callers see an unconditionally pure function. For @pure-unless-parameter-passed, PHPStan reports the by-ref parameter as pureFunction.parameterByRef. For @pure-unless-callable-is-impure, the body check exempts the $cb() call, so neither the body check nor the callers notice an impure callback, and no existing error covers that case.

Changes

• The new ConflictingPurityTagsRule resolves the docblock of a function or method with FileTypeMapper and reports each @pure-unless-* parameter when the same docblock has a purity tag: Function map() is marked as impure, which conflicts with @pure-unless-callable-is-impure for parameter $cb. (pureFunction.conflictingPurityTags / pureMethod.conflictingPurityTags). Aliases such as @psalm-pure, @impure and the @phpstan-pure-unless-* variants count.
• It reads the docblock as written, so tags inherited from a parent, interface or stub and the class-level @phpstan-all-methods-pure / -impure don't count. It covers interface, abstract, trait, enum and anonymous-class methods.
• It skips property hooks, where PHPStan reads @phpstan-pure but ignores @pure-unless-*, and closures, where neither tag applies. Like the other bleeding-edge rules, it doesn't validate stub files.
• For a docblock with both @phpstan-pure and @phpstan-impure, the message says "marked as pure", since ResolvedPhpDocBlock::isPure() prefers @phpstan-pure.
• It doesn't change how PHPStan treats such a function or method; it reports the docblock. Where pureFunction.parameterByRef or pureFunction.redundantUnlessCallable fire for the same docblock, both errors appear.
• It can report existing code, so I registered it on level 2 behind the reportConflictingPurityTags bleeding-edge toggle, next to PureFunctionRule and PureMethodRule. The config lines touch the same spot as Check the purity declarations of methods without a body #6668, so whichever merges second needs a rebase.