Adds a measured benchmark for the native data layer (Task 6).
## What
- New criterion bench `crates/wickra/benches/data_layer.rs` exercising the data layer on **50 000 real BTCUSDT 1m candles** (`examples/data/btcusdt-1m.csv`):
- **CSV parse** (`CandleReader`)
- **Tick aggregation** → 1m candles (`TickAggregator`)
- **Resample** 1m → 5m (`Resampler`)
- New **"4. Data layer"** section in `BENCHMARKS.md` with the measured numbers and the same "one core, FFI boundary" framing as the per-binding table.
## Measured (Rust core, Ryzen 9 9950X, median of 100 samples)
| Operation | Throughput | Per element |
|---|--:|--:|
| CSV parse | 3.0 M candles/s | 329 ns |
| Tick aggregate → 1m | 44 M ticks/s | 22.6 ns |
| Resample 1m → 5m | 234 M candles/s | 4.3 ns |
This is the same native code every binding rides through the FFI boundary characterised in §3 — the data I/O that replaces pandas / csv-parse / manual bucketing / pandas.resample, with zero third-party packages.
Run: `cargo bench -p wickra --bench data_layer`.
Verified locally: `cargo clippy -p wickra --benches --all-features -- -D warnings` clean; bench runs green.
kingchenc
2d2d5970b4