fix(audio): keep paused playback alive

[joeykchen]

Godot reports an active paused stream as not playing. Forwarding that value made the Go audio manager discard its playback ID before Resume, and allowed its wait/cleanup paths to treat the sound as finished. Make the engine query include the existing paused state, consistent with the backend's voice-retention rule, and document that lifetime contract on the Go Backend interface.

The second cleanup review keeps this to one backend expression and one contract comment. No Go paused-state mirror or additional helper is introduced. This engine-side fix requires a runtime built with the updated SPX module.

Validation:

• A real Godot C++ regression fails on the old backend only at the paused-lifetime assertions; after rebuilding the patched module, all 44 assertions pass without resource-leak diagnostics.
• Covers pause, update, resume, Stop, StopAll, stopped-player cleanup and audio-object destruction using real stream playback.
• Relevant Go audio/root tests, pure-engine checks and root wasm compilation pass.
• Runtime metadata is regenerated twice with identical output; the source-position metadata change is included.

[fennoai]

Reviewed the complete fixed range from 03576e6c0bbead9e73736482539dd321f5521206 through 546aeea343b36ee404f7fd87a9e772cf171fe9f9, including the Godot audio lifetime change, backend contract documentation, generated metadata, and regression coverage. The paused-state query is consistent with the existing cleanup logic, and the focused validation passed with go test ./internal/audio and git diff --check; no concrete, actionable findings remain.