Add batched row iteration via allBatched(batchSize)

[xoxohorses]

Description

Adds RowsIterator.nextBatch(maxRows) in Rust and exposes Statement.allBatched(batchSize, ...bindParameters) in the promise API.

This was motivated by a production trace of a simple ordered query that returned 9,088 rows: about 280 ms of its 350 ms p50 was attributed to SQLite processing. For that result size, the current all() path makes 9,088 asynchronous Rust-to-JavaScript round trips. Batching keeps SQLite's row-at-a-time stepping inside Rust and resolves one Promise per batch, which removes most of the boundary and Promise overhead.

Benchmark

The public benchmark prepares the table before timing, reads the same rows through each API, and validates every result. These averages were measured on Node 22.13.1 for x64 Linux with an Intel Xeon Platinum 8375C CPU.

Rows	all()	allBatched(250)	Speedup
1,000	15.213 ms	1.292 ms	11.77x
10,000	151 ms	11.417 ms	13.25x
100,000	1.535 s	164 ms	9.36x
1,000,000	15.780 s	1.132 s	13.94x

Benchmark source: https://github.com/xoxohorses/libsql-js/blob/e64ee564e60226e076c243342821ce90829158b5/perf/perf-libsql-batched-rows.js

How was this change tested?

• Automated test (unit, integration, etc.)
• Manual test (provide reproducible testing steps below)

Built the native module, then ran the public benchmark across 1,000, 10,000, 100,000, and 1,000,000 returned rows. The benchmark validated each result set.

[written by Codex]