cursor.bulkcopy() ignores connection timeout - pycore connection hardcodes 15s #626

Summary

This is a known gap, opening up issue in case someone faces this - registering as a bug.
The connection timeout parameter is not forwarded to the mssql-py-core TDS connection that cursor.bulkcopy() opens internally. mssql-py-core/src/connection.rs defaults to 15 seconds, and there is currently no way for users to override this value from Python.

Current behavior

1. connect(timeout=X) sets the ODBC query timeout. This applies to execute, fetch, etc. but has no effect on the separate connection that cursor.bulkcopy() opens through pycore.

2. connstr_to_pycore_params() in helpers.py drops connect_timeout from the key map, so it never reaches pycore.

3. The pycore side defaults to 15 seconds when connect_timeout is not provided. Users have no way to override this.

Expected behavior

The connection timeout should be forwarded from the Python side through connstr_to_pycore_params() to mssql_py_core.PyCoreConnection, allowing users to control how long the Rust TDS connection waits when establishing a connection to SQL Server.

Possibly related

This may be related to #595 (random "Timeout while connecting" errors during concurrent bulk loads on 1.7.1). The hardcoded 15-second timeout may be insufficient under heavy concurrent load, and users currently cannot increase it.