Reject StreamingTranscriber.connect on early socket failure

[RitwijParmar]

What

• Reject StreamingTranscriber.connect() if the socket errors before the Begin event.
• Reject StreamingTranscriber.connect() if the socket closes before the Begin event.
• Add unit coverage for both early-failure paths.

Why

Fixes #136. Today these pre-Begin failures only emit listeners, so await transcriber.connect() can remain pending indefinitely and callers cannot handle DNS/proxy/transport failures with try/catch or retry logic.

Verification

• git diff --check
• corepack pnpm@8.15.9 jest --config jest.unit.config.js tests/unit/streaming.test.ts --testTimeout 5000
• corepack pnpm@8.15.9 lint:tsc