Refactor JWT support for firebase/php-jwt ^7.0 and clean PHPUnit 13 output

[josbeir]

Summary

• Upgrades JWT dependency to firebase/php-jwt ^7.0 (now on v7.0.2).
• Adds explicit HMAC secret length validation in FirebaseTokenFactory:
  • HS256 >= 32 bytes
  • HS384 >= 48 bytes
  • HS512 >= 64 bytes
• Updates docs/config notes to document the new minimum secret lengths.
• Updates affected tests with compliant secrets and adds coverage for short-secret validation.

PHPUnit 13 cleanup

• Removes apc.enable_cli ini override from PHPUnit config to avoid runner warning.
• Replaces mock objects without expectations with stubs in middleware tests to remove PHPUnit notices.

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