fix: initialize _pollingEnabled from operationParams to prevent Linux crash

The _pollingEnabled flag was never being initialized from the query's
polling parameter (operationParams->polling). This caused Cancel() to
take the wrong code path on Linux:

- With _pollingEnabled=false, Cancel() called SQLCancelHandle() directly
- SQLCancelHandle() called concurrently with SQLExecDirectW caused a
  double-free crash on Linux (works on Windows)

Now _pollingEnabled is properly set from the operation params in the
constructor, so when polling mode is requested, the cooperative cancel
path is used (_cancelRequested flag) instead of direct SQLCancelHandle.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: TimelordUK

cpp/src/odbc/odbc_statement_legacy.cpp

@@ -202,6 +202,7 @@ OdbcStatementLegacy::OdbcStatementLegacy(
   // cerr << "OdbcStatement() " << _statementId << " " << endl;
   // fprintf(stderr, "OdbcStatement::OdbcStatement OdbcStatement ID = %ld\n ", statement_id);
   _numericStringEnabled = _operationParams->numeric_string;
+  _pollingEnabled.store(_operationParams->polling);
   _errors = make_shared<vector<shared_ptr<OdbcError>>>();
 }