Add raw WebSocket support to Web PubSub emulator

[Liangying.Wei (vicancy)]

Summary

• add the raw WebSocket client endpoint with access-key JWT validation
• keep group membership connection-scoped and authorize raw send-to-group operations from token roles
• manage active connection lifecycle with bounded, single-writer outbound delivery and slow-peer termination
• print startup connection guidance without exposing configured access keys
• document JSON and reliable protocols as deferred follow-up work

Validation

• Release build: 0 warnings, 0 errors
• Tests: 22 passed
• Packed and installed Microsoft.Azure.WebPubSub.Emulator 1.0.0-beta.1 as a local .NET tool
• Verified HEAD /api/health and JWT-authenticated raw text and binary fan-out against the installed tool