DX-113627: Make RunSqlQuery JSON-safe output

[maxlepikhin]

Codex implemented it and tested based on the feedback from Jorge:

The SQL is "SELECT * FROM reporting.telemetry.stg_telemetry_metrics WHERE LOWER(org_name) = 'mobilityware'" and it was originally created by ChatGPT but fails both with Claude and ChatGPT. The error is basically "Error executing tool RunSqlQuery: Error serializing to JSON: TypeError: 'float' object cannot be interpreted as an integer" for both LLMs. It runs fine with the Dremio AI Agent. I wrote an equivalent SQL and it worked fine on all agents (ChatGPT, Claude and the Dremio AI Agent).

Change in tests/conftest.py was required to run tests, otherwise they didn't run with python 3.12.

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