Stream large settlement CSV exports instead of building the full string in memory

[Jagadeeshftw]

📌 Description

Per the README, GET /api/v1/settlements?format=csv "ignores pagination and exports every matching, sorted row" — for a large settlement history, toCsv in src/utils/csv.ts currently builds the entire CSV string in memory before sending it, which doesn't scale and blocks the event loop during serialization.

🧩 Requirements and context

• Stream the CSV response row-by-row (e.g. via res.write per chunk) instead of materializing the full string.
• Preserve the exact same escaping behavior expected from the CSV-escaping fix elsewhere in this batch.
• Keep response headers (Content-Type, filename) identical to the current export.

🛠️ Suggested execution

• Add a streaming variant of the CSV writer in src/utils/csv.ts (or a new csvStream.ts) used by routes/settlements.ts.
• Add a test simulating a large settlement set and asserting the response streams incrementally (not just correctness of final content).
• Leave the anchors CSV export on the simple in-memory path unless it also proves large in practice.

✅ Acceptance criteria

• Large settlement CSV exports stream instead of blocking on a single large string build.
• Output content is byte-identical to the previous in-memory implementation for the same data.
• Test coverage for the streaming path.

🔒 Security notes

Reduces memory-exhaustion/DoS risk from a very large unpaginated export.

📋 Guidelines

• Minimum 95% test coverage
• Clear documentation
• Timeframe: 96 hours

[GBOYEE]

Hello! I'd love to pick this one up (Stream large settlement CSV exports instead of building the full st...). I'll implement the helper and integrate it. I'll open a PR referencing this shortly once assigned.

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #87)
2. Your PR will be reviewed by the AnchorNet-Org maintainers

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