perf: materialize query results once

[huytdps13400]

Summary

• materialize the hybrid results getter once when building the JS-compatible rows object
• make _array, length, and item(index) share that single materialized array
• cover getter reads plus 60, 1,000, and 10,000-row sync/async access, including NULL, BLOB, and out-of-range behavior

Fixes #310.

Why

results is a HybridObject getter that returns the native result vector by value. The previous rows.item(index) closure evaluated that getter for every item, so traversing N rows requested N additional full result vectors. Caching the first materialization preserves the public result shape while removing the quadratic copy pattern.

Benchmark

Synthetic getter-copy benchmark using Bun 1.3.14, six-column rows, one warm-up plus 20 measured iterations. The getter conservatively returns a shallow array copy; timings include wrapper construction and the named consumer.

Rows	Consumer	Main median / p95	This PR median / p95	Getter reads
60	full item() traversal	0.0112 / 0.0150 ms	0.000709 / 0.00504 ms	62 → 1
1,000	full item() traversal	0.579 / 1.002 ms	0.00250 / 0.00313 ms	1,002 → 1
10,000	full item() traversal	30.014 / 32.130 ms	0.01396 / 0.01504 ms	10,002 → 1

For direct _array and length consumers, getter reads drop from 2 to 1 at every size. At 10,000 rows their median wrapper-plus-access time drops from about 0.014 ms to 0.006–0.008 ms in the same conservative benchmark.

The committed real-device harness coverage also traverses all items for 60, 1,000, and 10,000 rows through both execute and executeAsync.

Verification

• bun typecheck
• bun lint
• bun sqlite build
• iOS simulator, Debug/Hermes: unit 35/35, TypeORM 1/1, sqlite-vec 35/35
• Android API 35 emulator, Debug/Hermes: unit 35/35, TypeORM 1/1, sqlite-vec 35/35
• Android assembleDebug succeeded across all configured ABIs
• regression test verified red on main (5 getter reads for two rows) and green on this branch (1 read)

bun sqlite test --runInBand is currently blocked before test discovery by the repository's React Native 0.85 preset migration (react-native now requires @react-native/jest-preset). The real React Native harness suites above pass on both platforms.