Fix reference leak and double-DECREF in pyodbc.drivers() (#1503)

[apoorvdarshan]

Summary

Fixes #1503. mod_drivers() (backing pyodbc.drivers()) had two reference-counting bugs around the Object RAII wrapper.

1. Leaked driver name after PyList_Append

Object name(PyUnicode_FromString((const char*)szDriverDesc));  // owns a new ref
if (PyList_Append(result, name.Get()) != 0)                    // keeps its own ref
    return 0;
name.Detach();   // clears the wrapper WITHOUT decref -> our ref leaks

PyList_Append increments the refcount, so the local reference should be released by ~Object(). Detach() prevents that, leaking one string per driver per call. Fix: drop the Detach().

2. Double-DECREF of result on the ODBC error path

Object result(PyList_New(0));
...
if (ret != SQL_NO_DATA) {
    Py_DECREF(result);   // decrefs the list but doesn't clear the wrapper
    return RaiseErrorFromHandle(...);   // ~Object() then decrefs it AGAIN
}

The manual Py_DECREF plus the destructor double-frees the list on the driver-manager error path. Fix: drop the manual Py_DECREF and let ~Object() release it once.

Verification

Leak (bug 1), built locally against unixODBC with three dummy drivers, using sys.getallocatedblocks():

build	block growth over 20 000 drivers() calls
master	60001 (3 per call = one per driver)
this PR	1 (~0)

pyodbc.drivers() still returns the same list. Bug 2 is on the ODBC error path (hard to trigger without a broken driver manager), but the double-DECREF follows directly from the Object wrapper semantics — the destructor already releases result.

Disclosure: prepared with AI assistance; reviewed and verified locally.