Extract runtime state into a dedicated Context

[kettasoft]

Summary

Extract transient Filterable state into a dedicated runtime Context while preserving the existing public API and behavior.

Changes

• Add a dedicated final Runtime\Context class
• Move builder, request data, applied payloads, skipped payloads, and cache key generator state into Context
• Delegate existing Filterable state methods to the runtime Context
• Preserve applied and skipped Payload snapshots
• Keep validation and cache generation based on complete runtime data
• Synchronize Context with builders returned by initially() and finally()
• Throw MissingBuilderException when no builder is available
• Isolate runtime state between cloned Filterable instances
• Clone and rebind Engines when cloning filters
• Update fluent builder forwarding to use the Context-backed builder
• Add regression tests for Context state, cloning, caching, validation, and builder lifecycle