[Cleanup] Remove deprecated code after distributed architecture migration

[zhexuany]

Summary

Track code cleanup tasks after the distributed architecture is fully implemented.

Parent Epic

• [Epic] Distributed Roboflow with Alibaba Cloud (OSS + ACK) #9 Distributed Roboflow with TiKV Coordination

When to Execute

After all distributed features are complete and tested (Phase 10+)

Code to Remove

1. TiKV Backup Directory

• Delete crates/roboflow-distributed/src/tikv_backup/ (duplicate of tikv/)

Code to Refactor

2. OssStorage Full-Object Buffering

• crates/roboflow-storage/src/oss.rs lines 213-239
• Replace bytes().await.to_vec() with streaming reader
• Depends on: [Phase 6.1] Add streaming S3 reader with range requests #45 (Streaming S3 reader)

3. Sequential Multipart Uploads

• crates/roboflow-storage/src/multipart.rs lines 281-337
• Implement parallel part uploads
• Depends on: [Phase 6.2] Add parallel multipart uploads #46 (Parallel multipart uploads)

4. Sequential Batch Processing

• crates/roboflow-pipeline/src/fluent/builder.rs lines 439-456
• Replace sequential loop with TiKV job integration
• Depends on: [Phase 4.4] Implement Worker loop with job claiming #43 (Worker loop)

5. Sequential Reader Usage

• crates/roboflow-pipeline/src/orchestrator/orchestrator.rs lines 398-403
• Enable parallel readers

Code to Deprecate

6. Python Examples

• Add deprecation warning to examples/python/roboflow_utils.py::BatchProcessor
• Add deprecation notice to examples/python/batch_conversion.py
• Document migration path to distributed CLI

TODOs to Address

• crates/roboflow-pipeline/src/fluent/builder.rs line 397 - Standard pipeline
• crates/roboflow-pipeline/src/fluent/builder.rs lines 543, 596, 609, 657, 672, 690
• examples/rust/lerobot_convert.rs lines 51, 73, 92
• tests/kps_integration_tests.rs line 18

Tests to Update

• tests/sequential_parallel_comparison_tests.rs - Add distributed tests
• tests/pipeline_round_trip_tests.rs - Add job processing tests
• tests/streaming_converter_tests.rs - Add distributed streaming tests

Acceptance Criteria

• No duplicate code remains
• Full-object buffering replaced with streaming
• Sequential uploads replaced with parallel
• Batch processing uses TiKV queue
• Deprecated code has warnings
• All TODOs addressed or tracked
• Tests updated for distributed architecture