Add hasRelationPath method for relation path validation

[kettasoft]

Overview

This pull request introduces a new helper method hasRelationPath to the
Filterable core. It provides a reliable way to check if a given dot-notated
path refers to a valid relation.

Changes

• Added hasRelationPath(string $path): bool method.
• Supports nested relations using dot notation (e.g. user.posts.comments).
• Handles both associative and flat relations arrays.
• Improves overall safety when resolving relation-based filters.