Concurrent writes in SQLRite: shipping BEGIN CONCURRENT and MVCC in v0.10.0

SQLRite v0.10.0 lifts the single-writer ceiling. The release ships an in-memory version index, BEGIN CONCURRENT with row-level conflict detection at commit, snapshot-isolated reads, durable WAL log-records, and sibling connection handles across every SDK — Rust, Python, Node, Go, C FFI, and a REPL demo.