[JDBC] Implement DataSource login timeout #1267

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.

Related DriverManager work: #1268