Adjust binding code generator to fix UnicodeError

This change addresses a UnicodeError in the MicroPython-LVGL binding generator
by explicitly handling `char *` arguments in `build_callback_func_arg`.

Previously, the function relied on the `lv_to_mp` dictionary for all type
conversions, which could lead to incorrect or missing converters for `char *`,
causing encoding issues. Now, `char *` arguments are assigned the `ptr_to_mp`
converter directly, ensuring proper conversion to MicroPython string objects.

Additionally, the initial type extraction preserves qualifiers
(`remove_quals=False`) to improve type handling accuracy, while maintaining
compatibility for non-`char *` types by stripping qualifiers in the fallback
path.

Author: ThomasFarstrike

gen/python_api_gen_mpy.py

@@ -2865,12 +2865,18 @@ def create_helper_struct(struct_str):
 
 
 def build_callback_func_arg(arg, index, func, func_name = None):
-    arg_type = get_type(arg.type, remove_quals = True)
+    arg_type = get_type(arg.type, remove_quals = False)
     cast = '(void*)' if isinstance(arg.type, c_ast.PtrDecl) else '' # needed when field is const. casting to void overrides it
-    if arg_type not in lv_to_mp or not lv_to_mp[arg_type]:
-        try_generate_type(arg.type)
+
+    if arg_type == 'char *':
+        converter = 'ptr_to_mp'
+    else:
+        arg_type = get_type(arg.type, remove_quals = True)
         if arg_type not in lv_to_mp or not lv_to_mp[arg_type]:
-            raise MissingConversionException("Callback: Missing conversion to %s" % arg_type)
+            try_generate_type(arg.type)
+            if arg_type not in lv_to_mp or not lv_to_mp[arg_type]:
+                raise MissingConversionException("Callback: Missing conversion to %s" % arg_type)
+        converter = lv_to_mp[arg_type]
 
     arg_metadata = {'c_type': arg_type, 'py_type': get_py_type(arg_type)}
 
@@ -2880,8 +2886,9 @@ def build_callback_func_arg(arg, index, func, func_name = None):
         arg_metadata['name'] = None
 
     callback_metadata[func_name]['args'].append(arg_metadata)
+
     return 'mp_args[{i}] = {convertor}({cast}arg{i});'.format(
-                convertor = lv_to_mp[arg_type],
+                convertor = converter,
                 i = index, cast = cast)