Fix: Simplify json_set schema to avoid anyOf operator

[vchomakov]

Problem

The JsonValue class was added to address Gemini tool exclusion issues, but it inadvertently caused the nested anyOf schema problem described in jlowin/fastmcp#1871. This nested anyOf structure breaks LLM clients' ability to properly parse and use the tool.

Solution

• Remove the JsonValue class
• Use simple str type for the value parameter instead
• Add JSON parsing logic with graceful fallback:
  • Tries to parse input as JSON with json.loads()
  • Falls back to treating it as a plain string if parsing fails
  • Passes the result to Redis

Result

Generates a clean {"type": "string"} schema instead of nested anyOf. Verified with the latest Gemini version that tool exclusion no longer occurs.

[bobymicroby]

lgtm