feat(bench): add SQLite pool benchmarks for #158

[mmustafasenoglu]

Summary

Adds criterion benchmarks covering the core performance scenarios described in #158:

Benchmark	Description
connect	Establish a new SQLite connection
pool_checkout	Acquire an idle connection from the pool
ping	Ping an existing connection
query_small	TechEmpower-style single-row query (3 columns)
query_large_10k	Stream 10K rows with 5 columns (i32, i64, f64, String, BLOB)

Design

• Uses in-memory SQLite — no external database required to run benchmarks.
• Seeds 10,000 rows via a recursive CTE for the large-result benchmark.
• Follows the existing benches/sqlite/describe.rs pattern (Criterion + async_tokio).
• Registered in Cargo.toml as [[bench]] with harness = false.

Running

cargo bench --bench sqlite-simple --features sqlite

Closes #158