v1.62-python3-rc1: Python 3 support

Python 3 host environment execution support

Issue 1 — Settings API ✅

• Restored globalSettings.getBoolean() for show-eol and visible-whitespace
• enginePreference and python3Path correctly use loadExtensionSetting / saveExtensionSetting (in-panel UI controls, not registered with globalSettings)
• Fixed Python3Runner to load python3Path via callbacks.loadExtensionSetting

Issue 2 — JSON parsing ✅

• Replaced hand-rolled JSON parser with com.google.gson:gson:2.11.0
• Gson().toJson() for serialization, JsonParser.parseString() for deserialization

Issue 3 — Duplicate API signature concern ✅

• Added prominent # !! SYNC: comments above RequestEngine.__init__ in both ScriptEnvironment.py (Jython) and turbo_intruder.py (Python 3), each pointing to the other
• Added matching comments in fast-http.kt and Python3Runner.kt at the call sites
• Added ## API SYNC RULE section to AGENTS.md with a full step-by-step checklist for what to update when a Kotlin engine parameter changes

Also fixed (pre-existing)

• BurpRequestEngine: guarded null HTTP response to fix silent NPE dropping all responses in BURP2/gate race attacks