convert-hf : use a plain class for Model, and forbid direct instantiation

There are no abstract methods used anyway,
so using ABC isn't really necessary.

convert-hf-to-gguf.py

@@ -8,7 +8,6 @@ import json
 import os
 import re
 import sys
-from abc import ABC
 from enum import IntEnum
 from pathlib import Path
 from hashlib import sha256
@@ -41,7 +40,7 @@ class SentencePieceTokenTypes(IntEnum):
 AnyModel = TypeVar("AnyModel", bound="type[Model]")
 
 
-class Model(ABC):
+class Model:
     _model_classes: dict[str, type[Model]] = {}
 
     dir_model: Path
@@ -62,6 +61,8 @@ class Model(ABC):
     model_arch: gguf.MODEL_ARCH
 
     def __init__(self, dir_model: Path, ftype: int, fname_out: Path, is_big_endian: bool, use_temp_file: bool):
+        if self.__class__ == Model:
+            raise TypeError(f"{self.__class__.__name__!r} should not be directly instantiated")
         self.dir_model = dir_model
         self.ftype = ftype
         self.fname_out = fname_out
@@ -78,6 +79,13 @@ class Model(ABC):
         self.tensor_map = gguf.get_tensor_name_map(self.model_arch, self.block_count)
         self.tensors = dict(self.get_tensors())
 
+    @classmethod
+    def __init_subclass__(cls):
+        # can't use an abstract property, because overriding it without type errors
+        # would require using decorated functions instead of simply defining the property
+        if "model_arch" not in cls.__dict__:
+            raise TypeError(f"Missing property 'model_arch' for {cls.__name__!r}")
+
     def find_hparam(self, keys: Iterable[str], optional: bool = False) -> Any:
         key = next((k for k in keys if k in self.hparams), None)
         if key is not None:
@@ -266,8 +274,6 @@ class Model(ABC):
 
         def func(modelcls: AnyModel) -> AnyModel:
             for name in names:
-                if "model_arch" not in modelcls.__dict__:
-                    raise TypeError(f"Missing property 'model_arch' for {modelcls.__name__!r}")
                 cls._model_classes[name] = modelcls
             return modelcls
         return func