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.

This package requires no ibexa/core dependency of its own (it is a standalone Composer plugin), so pulling in ibexa/phpstan (which requires ibexa/core) needed "minimum-stability": "dev" / "prefer-stable": true added to composer.json to let Composer resolve the dev-only ibexa/core version; this pattern already exists in other tool-style packages such as ibexa/doctrine-schema and ibexa/migrations.

No dynamic calls to static methods were found in this package (0 hits, confirmed with the staticMethod.dynamicCall strict rule temporarily enabled and sanity-checked against a synthetic fixture), so no second commit was needed. The staticMethod.dynamicCall strict rule itself is enabled in the linked ibexa/phpstan PR; this PR keeps CI green once that is released.

ibexa/phpstan's existing rules (Ibexa.requireClosureReturnType, Ibexa.noConfigResolverParametersInConstructor) also reported 0 new errors against this package's src, so no third commit was needed either.

Note: this package has no tests/ directory and its composer.json test script (phpunit -c phpunit.xml) does not currently resolve to a working binary; both are pre-existing conditions on 6.0, unrelated to this change.

For QA:

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

Documentation:

No client-facing impact.