Fix: added KV to transcoder-worker for idempotency

[Vchen7629]

• chore(scene-detector): reduced KV TTL from 7 days to 3 hours
• feat(transcoder-worker): created idempotency kv helper functions
• feat(transcoder-worker): updated subscriber.go with the idempotency KV check and add
• feat(transcoder-worker): updated main.go to create the idempotency kv
• fix(transcoder-worker): fixed fmt error formatting in chunk_kv.go
• chore(transcoder-worker): updated error msgs
• tests(transcoder-worker): created unit/integration tests for chunk_kv.go and updated subscriber and main.go
• tests(backend): added idempotency pipeline tests for all 3 services