NotImplementedError when calling AutoTokenizer from ctransformers package
Author: heiko-braun
Pull request: no

### System Info

```
Python 3.10.8

transformers==4.34.1
ctransformers==0.2.27
```

I am tinkering with  `TheBloke/Mistral-7B-Instruct-v0.1-GGUF`, but when calling AutoTokenizer, I run into a `NotImplementedError `



### Who can help?

_No response_

### Information

- [X] The official example scripts
- [ ] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

```
from ctransformers import AutoModelForCausalLM, AutoTokenizer

model_name = "TheBloke/Mistral-7B-Instruct-v0.1-GGUF"
model_file = "mistral-7b-instruct-v0.1.Q4_K_M.gguf"

model = AutoModelForCausalLM.from_pretrained(
    model_name, 
    model_file=model_file, 
    model_type="mistral", 
    gpu_layers=0,
    hf=True
    )
```

When trying to instantiate a tokeniser, I run into this issue:

```
tokenizer = AutoTokenizer.from_pretrained(model)
```

Error:
```
NotImplementedError                       Traceback (most recent call last)
[/workspaces/codespaces-jupyter/notebooks/summarise.ipynb](https://0vudeajo4kvkl20agapvl4rui237bovpe0k8r5lq5al4to17l0hk.assets.github.dev/workspaces/codespaces-jupyter/notebooks/summarise.ipynb) Cell 4 line 2
      <a href='vscode-notebook-cell://codespaces%2Bhumble-dollop-9x4wqpqp2jww/workspaces/codespaces-jupyter/notebooks/summarise.ipynb#W3sdnNjb2RlLXJlbW90ZQ%3D%3D?line=0'>1</a> #Tokenizer
----> <a href='vscode-notebook-cell://codespaces%2Bhumble-dollop-9x4wqpqp2jww/workspaces/codespaces-jupyter/notebooks/summarise.ipynb#W3sdnNjb2RlLXJlbW90ZQ%3D%3D?line=1'>2</a> tokenizer = AutoTokenizer.from_pretrained(model)

File [~/.python/current/lib/python3.10/site-packages/ctransformers/hub.py:268](https://0vudeajo4kvkl20agapvl4rui237bovpe0k8r5lq5al4to17l0hk.assets.github.dev/stable/f1b07bd25dfad64b0167beb15359ae573aecd2cc/out/vs/workbench/contrib/webview/browser/pre/~/.python/current/lib/python3.10/site-packages/ctransformers/hub.py:268), in AutoTokenizer.from_pretrained(cls, model)
    261 if not isinstance(model, CTransformersModel):
    262     raise TypeError(
    263         f"Currently `AutoTokenizer.from_pretrained` only accepts a model object. Please use:\n\n"
    264         "  model = AutoModelForCausalLM.from_pretrained(..., hf=True)\n"
    265         "  tokenizer = AutoTokenizer.from_pretrained(model)"
    266     )
--> 268 return CTransformersTokenizer(model._llm)

File [~/.python/current/lib/python3.10/site-packages/ctransformers/transformers.py:84](https://0vudeajo4kvkl20agapvl4rui237bovpe0k8r5lq5al4to17l0hk.assets.github.dev/stable/f1b07bd25dfad64b0167beb15359ae573aecd2cc/out/vs/workbench/contrib/webview/browser/pre/~/.python/current/lib/python3.10/site-packages/ctransformers/transformers.py:84), in CTransformersTokenizer.__init__(self, llm, **kwargs)
     83 def __init__(self, llm: LLM, **kwargs):
---> 84     super().__init__(**kwargs)
     85     self._llm = llm

File [~/.python/current/lib/python3.10/site-packages/transformers/tokenization_utils.py:367](https://0vudeajo4kvkl20agapvl4rui237bovpe0k8r5lq5al4to17l0hk.assets.github.dev/stable/f1b07bd25dfad64b0167beb15359ae573aecd2cc/out/vs/workbench/contrib/webview/browser/pre/~/.python/current/lib/python3.10/site-packages/transformers/tokenization_utils.py:367), in PreTrainedTokenizer.__init__(self, **kwargs)
    363 super().__init__(**kwargs)
    365 # 4. If some of the special tokens are not part of the vocab, we add them, at the end.
    366 # the order of addition is the same as self.SPECIAL_TOKENS_ATTRIBUTES following `tokenizers`
--> 367 self._add_tokens(
...
   1675         `Dict[str, int]`: The vocabulary.
   1676     """
-> 1677     raise NotImplementedError()
```

### Expected behavior

Successful instatiation of a tokeniser

Comments:
It seems to bump off https://github.com/marella/ctransformers/blob/main/ctransformers/transformers.py#L84 into https://github.com/huggingface/transformers/blob/main/src/transformers/tokenization_utils.py#L367, but I don't see where it runs into the NotImplementedError

Maybe it's realted to https://github.com/marella/ctransformers/issues/154?

Closing this one in favour of https://github.com/marella/ctransformers/issues/154