fix(media): restore Media state on unserialize from Doctrine cache

[BriceFab]

Summary

• add Media::__unserialize() so cached Media instances restore typed properties correctly
• keep backward compatibility with legacy indexed payloads ([0 => path, 1 => library])
• register Media::$resolverInitializer in bundle boot (same resolver used by Doctrine media types)
• add regression tests for serialize/unserialize behavior

Problem

When an entity containing JoliCode\MediaBundle\Model\Media is read from Doctrine second-level cache, unserialization may create dynamic properties ($0, $1) instead of restoring constructor-backed typed properties.

This can leave $path uninitialized and later crash at runtime when getPath() is accessed.

Validation

• added tests in tests/src/Model/MediaTest.php for:
  • serialize/unserialize roundtrip
  • legacy indexed payload support
• syntax checks on modified files

Fixes #87

cc @xavierlacot