[codex] realtime warmup start

[eilon-decart]

Summary

• Adds client.realtime.warmup(options) and RealTimeWarmupClient.start(stream).
• Opens the bouncer/LiveKit session with livekit_warmup=1 and delays local track publishing until start().
• Reuses the existing mirror and codec publish path for delayed start.
• Keeps client.realtime.connect(stream, options) unchanged.

Validation

• pnpm --dir /Users/eilon/Development/sdk/packages/sdk exec vitest run tests/realtime.unit.test.ts
• pnpm --dir /Users/eilon/Development/sdk/packages/sdk exec tsc --noEmit
• pnpm --dir /Users/eilon/Development/sdk/packages/sdk exec biome check src/realtime/client.ts src/realtime/media-channel.ts src/realtime/stream-session.ts src/index.ts tests/realtime.unit.test.ts

[pkg-pr-new]

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npm i https://pkg.pr.new/@decartai/sdk@150

commit: fb8d254