feat(jdbc): JdbcExporter, matching the CSV and Parquet exporters #567

vortex-jdbc only has JdbcImporter/JdbcImportOptions; csv and parquet each have an importer and an exporter. Add JdbcExporter + JdbcExportOptions for symmetry: read a Vortex file and move its rows into a table in a JDBC database over a caller-supplied Connection.

API sketch

JdbcExportOptions opts = JdbcExportOptions.defaults()
        .withBatchSize(5_000)
        .withBinder(JdbcBinder.standard()
                .with(DType.Extension.class, (ps, i, value) -> ps.setObject(i, value)));

JdbcExporter.export(vortexPath, connection, "ohlc", opts);

• Options are a final class with a private constructor, defaults() and withXxx copies, as everywhere else. The target table is a required argument of export, not an option (confirm that CsvExporter/ParquetExporter take their target the same way).
• Binder (callback): a small functional interface that sets one value on a PreparedStatement. JdbcBinder.standard() covers primitives, strings, decimals, booleans and dates. A user overrides only the types their database needs special handling for (Postgres arrays, setObject for timestamps).
• DDL helper, not automatic: a DType to SQL type function plus createTableSql(name, dtype) returns a CREATE TABLE string. The exporter never creates or alters a table on its own; creation is opt-in.

Behavior

• Appends to an existing table with INSERT INTO t (cols...) VALUES (?, ...) through a PreparedStatement. Nulls follow the validity mask.
• One transaction for the whole export: remember the connection's auto-commit setting, setAutoCommit(false), addBatch() per row, executeBatch() every batchSize rows, commit() at the end, rollback() and rethrow on failure, and restore auto-commit in a finally. The connection belongs to the caller. A failed export leaves nothing behind.
• ProgressListener, as in the other exporters.

Open design questions

• Reverse type mapping DType to SQL type (the inverse of SqlTypeToDType); it varies by database.
• Create-if-missing vs truncate vs fail-if-exists: all opt-in, append is the default.
• A withCommitEvery(n) option for very large exports, if a long-lived transaction proves a problem. Not in the first cut.

Not needed for the jdbc:vortex: driver work (#566). No demand yet, so this waits until someone needs it.