fix: add isValidClassInstance method to detect serialized class instances

[htafolla]

Summary

Fixes the bug where processorManager.executePreProcessors is not a function error occurs when using the StrRay Codex Injection plugin.

Root Cause

When the ProcessorManager class instance is stored in the StringRayStateManager with JSON persistence enabled, it gets serialized to JSON and loses its prototype chain. Upon retrieval, the object is just a plain JavaScript object without any class methods, causing the "is not a function" errors.

Solution

1. Added isValidClassInstance() method - New method on StringRayStateManager that checks if a stored value is a valid class instance by verifying the presence of expected methods and detecting plain objects that lost their prototype.

2. Enhanced logging in get() - Added valueType to the log output for debugging purposes.

Changes

• src/state/state-manager.ts: Added isValidClassInstance(value, methodName) method and enhanced get() logging

Testing

The fix was validated in the Zigzag project by:

1. Adding validation in the plugin to check if executePreProcessors method exists before using the retrieved object
2. Creating fresh ProcessorManager instances instead of trying to reuse serialized ones

This ensures backward compatibility while providing a utility method for consumers to detect invalid class instances.

[htafolla]

Closing this PR - the changes are already incorporated into master (v1.15.38). The isValidClassInstance method is not needed as a standalone utility since the state manager handles class instances properly through the existing serialization/deserialization flow.