gh-129928: Rework sqlite3 error helpers (#129929)

Add a helper for raising DB-API compatible exceptions based on the
result code of SQLite C APIs. Some APIs do not store the error indicator
on the database pointer, so we need to be able to deduce the DB-API
compatible exception directly from the error code.

- rename _pysqlite_seterror() as set_error_from_db()
- introduce set_error_from_code()

Modules/_sqlite/util.c

@@ -118,18 +118,31 @@ exit:
     Py_XDECREF(exc);
 }
 
+void
+set_error_from_code(pysqlite_state *state, int code)
+{
+    PyObject *exc_class = get_exception_class(state, code);
+    if (exc_class == NULL) {
+        // No new exception need be raised.
+        return;
+    }
+
+    const char *errmsg = sqlite3_errstr(code);
+    assert(errmsg != NULL);
+    raise_exception(exc_class, code, errmsg);
+}
+
 /**
  * Checks the SQLite error code and sets the appropriate DB-API exception.
- * Returns the error code (0 means no error occurred).
  */
-int
-_pysqlite_seterror(pysqlite_state *state, sqlite3 *db)
+void
+set_error_from_db(pysqlite_state *state, sqlite3 *db)
 {
     int errorcode = sqlite3_errcode(db);
     PyObject *exc_class = get_exception_class(state, errorcode);
     if (exc_class == NULL) {
-        // No new exception need be raised; just pass the error code
-        return errorcode;
+        // No new exception need be raised.
+        return;
     }
 
     /* Create and set the exception. */
@@ -137,7 +150,6 @@ _pysqlite_seterror(pysqlite_state *state, sqlite3 *db)
     // sqlite3_errmsg() always returns an UTF-8 encoded message
     const char *errmsg = sqlite3_errmsg(db);
     raise_exception(exc_class, extended_errcode, errmsg);
-    return extended_errcode;
 }
 
 #ifdef WORDS_BIGENDIAN