IBX-12654: Added ibexa/phpstan and fixed dynamic calls to static methods

[bnowak]

🎫 Issue	IBX-12654

Related PRs:

• IBX-12654: Enabled the PHPStan strict rule for dynamic calls to static methods phpstan#16

Description:

Adds ibexa/phpstan as a dev dependency and includes its extension in the PHPStan configuration.
Replaces dynamic calls to static methods ($this->assertX(), static test helpers, ...) with self::/ClassName:: calls: 33 calls in 11 files. The staticMethod.dynamicCall strict rule itself is enabled in the linked ibexa/phpstan PR; this PR keeps CI green once that is released.
Also fixes what the existing ibexa/phpstan rules report: 3 closures/arrow functions got return types (Ibexa.requireClosureReturnType).

Judgment call: converting one dynamic $this->assertInstanceOf() call (inside a closure in tests/lib/Validator/Constraint/PasswordValidatorTest.php) to self::assertInstanceOf() changed which PHPStan identifier a pre-existing "always evaluate to true" false positive is reported under (method.alreadyNarrowedType → staticMethod.alreadyNarrowedType), since it now merges with an already-baselined occurrence of the same message. The stale method.alreadyNarrowedType baseline entry (no longer matched) was removed and the sibling staticMethod.alreadyNarrowedType entry's count was updated from 1 to 2 to reflect the two identical, pre-existing occurrences now sharing one identifier. No error is newly ignored; this is purely a mechanical reclassification caused by the self:: conversion.

For QA:

No functional change. CI (PHPStan, code style, unit tests) is the verification.

Documentation:

No client-facing impact.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud