[JDBC] Implement DataSource login timeout

### Describe the enhancement requested

`ArrowFlightJdbcDataSource.setLoginTimeout(int)` currently throws `SQLFeatureNotSupportedException`, and `getLoginTimeout()` always returns `0`.

Implement the JDBC `DataSource` login-timeout contract:

- Store and return the timeout configured for each `ArrowFlightJdbcDataSource` instance.
- Apply a nonzero timeout to connection establishment through `DataSource.getConnection()`.
- Preserve the JDBC semantics of zero: use the default system timeout if one exists; otherwise, do not impose a timeout.
- If the timeout expires, attempt to cancel the connection attempt and throw `SQLTimeoutException`.
- Clean up any allocator, channel, or partially constructed client when the attempt is cancelled or times out.
- Add tests for the default value, setter/getter behavior, timeout enforcement, exception type, and resource cleanup.

This is distinct from #494/#495. The existing `connectTimeoutMs` property configures Netty socket connection attempts; the JDBC login timeout applies to the overall database connection attempt exposed by `DataSource.getConnection()`.

Context: #1027 and [the follow-up discussion](https://github.com/apache/arrow-java/pull/1027#issuecomment-5447203124).

Related DriverManager work: https://github.com/apache/arrow-java/issues/1268

Start with ArrowFlightJdbcDataSource.setLoginTimeout(int), getLoginTimeout(), and the DataSource.getConnection() path; compare them with the existing connectTimeoutMs behavior. Add coverage for the default, setter/getter, timeout enforcement, SQLTimeoutException, and cleanup of partially created resources. Done means zero preserves default behavior and nonzero login timeouts cancel failed attempts without leaks.

Vom Indexierungsmodell aus dem Issue-Text verfasst.