Replace ObjectMapper with PythonObject

[maksymuimanov]

Replace all JSON-based serialization/deserialization (currently handled via ObjectMapper) with direct Java - Python object mapping, so that:

Java method arguments and return values are transferred as native Python objects (lists, dicts, primitives, etc.);

• No intermediate JSON encoding/decoding happens;
• Communication can rely on binary, pickle, or Py4J-level structures.

Currently, the design looks like:

• Java side converts objects - JSON (via Jackson ObjectMapper);
• Sends JSON to Python via REST/gRPC;
• Python deserializes JSON - Python dict;
• Then the reverse process happens in response.

This adds double serialization overhead, causes loss of type fidelity, and limits performance.