feat: End-to-end integration test with Postgres and data generation

[soniapi]

This adds a complete native Rust integration test in tests/integration_test.rs. It spins up a PostgreSQL container using testcontainers, applies diesel migrations, sets up partitioned tables split by 180,000 using divider, natively generates 200,000 mock rows (ASK, BID, TRADE distribution) to an Excel file using rust_xlsxwriter, and feeds it to fill_partitions via a minimal built binary. Finally, it calculates mid-prices (mp) and costs (c) for all TRADE objects dynamically and updates the c column correctly in the DB.

Replaced all initial Python generation with pure Rust implementation to satisfy requirements.

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PR created automatically by Jules for task 16637349897707855644 started by @soniapi

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