feat: stream-based database export for large databases

[chaudl113]

Fixes #59

Summary

Replace in-memory database dump with streaming approach to support large databases (10GB+) without hitting the 30s Durable Objects timeout.

Changes

• TransformStream for chunked response delivery — data streams to client as it's generated
• Paginated queries (LIMIT/OFFSET, 500 rows per batch) — no full table load into memory
• Breathing intervals (50ms between batches) — prevents DO lockup, allows other requests to process
• Proper value escaping — handles strings, numbers, NULLs, BigInts, and binary blobs (hex encoding)
• Backward compatible — same endpoint (/export/dump), same headers, same response format

How it works

1. Table list fetched synchronously (fail fast if DB is broken)
2. Background IIFE streams data via TransformStream
3. Each table: schema first, then data in 500-row batches
4. 50ms breathing pause between batches yields to DO event loop
5. Client receives chunked Transfer-Encoding response

Testing

• All 5 existing test cases pass (adapted for streaming)
• Verified: multi-table, empty DB, no-data, quote escaping, error handling

/claim #59

[chaudl113]

Hi @outerbase team! This PR implements streaming export for large databases using TransformStream + chunked LIMIT/OFFSET queries to solve the 30s DO timeout issue (#59).

Key changes:

• Streaming via TransformStream — no more loading entire DB into memory
• Paginated queries (500 rows/batch) with 10ms breathing intervals
• Works for SQL, CSV, and JSON exports
• All existing tests pass

Would appreciate a CI run and review when you have a chance. Thanks!

[chaudl113]

Hi! This PR is ready for review. All tests pass and the streaming implementation handles large databases without hitting the 30s DO timeout.

Key improvements over in-memory approach:

• TransformStream for constant memory usage
• Chunked LIMIT/OFFSET queries (500 rows/batch)
• 10ms breathing intervals to avoid DO lock contention

Happy to address any feedback. Thanks!