feat(voice): VoiceToolCallSession + extract CAS URL/auth helpers

[JoshParkSJ]

Summary

• Adds `VoiceToolCallSession` (new `packages/uipath/src/uipath/_cli/_chat/_voice_session.py`): persistent socket.io connection to CAS that receives batched `voice_tool_call` events, dispatches each call to a caller-supplied handler in parallel, and emits one `voice_tool_result` per `callId`. Exits on `voice_agent_completed` or socket disconnect, with a shutdown drain for in-flight tool tasks.
• Extracts `build_cas_url(context)` and `build_cas_auth_headers(context)` from the inline logic in `get_chat_bridge()`. `get_chat_bridge()` now delegates to these helpers — no behavior change.
• Both URL/auth helpers exported from `all` so the voice session runtime in `uipath-agents-python` can reuse them directly, avoiding duplicating the URL construction and auth header logic.

Context

The voice URT session runtime (`uipath_agents/voice/session.py`, see UiPath/uipath-agents-python#419) connects to CAS via the same socket.io endpoint as the chat bridge. Rather than duplicating the URL + auth setup, it calls `build_cas_url` and `build_cas_auth_headers` from this package, and drives the tool-call loop through `VoiceToolCallSession`.

Paired with: UiPath/AgentInterfaces#911 (CAS side) and UiPath/uipath-agents-python#419 (agent wiring).

Test plan

• Existing conversational agent flows unaffected (`get_chat_bridge` behavior unchanged)
• `build_cas_url` returns correct URL/path for both `CAS_WEBSOCKET_HOST` (local dev) and `UIPATH_URL` (prod)
• `build_cas_auth_headers` returns correct headers with token, tenant, org, and conversation ID
• `VoiceToolCallSession`: parallel tool calls dispatch concurrently; `voice_agent_completed` triggers drain + disconnect; connect timeout raises `VoiceToolCallSessionError`