Fix bos/eos token IDs + add enable_thinking to chat template

## Summary

Fix token configuration and add `enable_thinking` support for the chat template.

### Token ID fixes

The current `bos_token` and `eos_token` are both set to `<|endoftext|>` (id=0), which is incorrect for a ChatML-style model. This PR fixes them to match the actual chat format:

| Field | Before | After |
|-------|--------|-------|
| `bos_token` | `<\|endoftext\|>` (0) | `<\|im_start\|>` (1) |
| `eos_token` | `<\|endoftext\|>` (0) | `<\|im_end\|>` (2) |
| `bos_token_id` | 0 | 1 |
| `eos_token_id` | 0 | 2 |

These are also set in `config.json`.

(Subsumes PRs #3, #4, #5)

### `enable_thinking` chat template support

The Ouro-Thinking model enters chain-of-thought reasoning mode when `<think>` is prepended to the assistant turn, but the current chat template does not support triggering this.

This PR adds `enable_thinking` parameter support (following the convention from Qwen3 and DeepSeek-R1), so that:

```python
tokenizer.apply_chat_template(messages, add_generation_prompt=True, enable_thinking=True)
# produces: ...<|im_start|>assistant\n<think>\n
```

**Backward compatible** — default behavior is unchanged (no `<think>` unless explicitly requested).

This also enables proper integration with `vLLM` and `lm-eval-harness`, which pass `enable_thinking=True` to `apply_chat_template()`.

config.json

@@ -8,8 +8,8 @@
     "AutoModelForCausalLM": "modeling_ouro.OuroForCausalLM",
     "AutoModel": "modeling_ouro.OuroModel"
   },
-  "bos_token_id": 0,
-  "eos_token_id": 0,
+  "bos_token_id": 1,
+  "eos_token_id": 2,
   "head_dim": 128,
   "hidden_act": "silu",
   "hidden_size": 2048,
@@ -59,4 +59,4 @@
   "use_cache": true,
   "use_sliding_window": false,
   "vocab_size": 49152
-}
+}

tokenizer_config.json

@@ -157,8 +157,8 @@
     "<jupyter_script>",
     "<empty_output>"
   ],
-  "bos_token": "<|endoftext|>",
-  "chat_template": "{%- if messages[0]['role'] == 'system' -%}{{- '<|im_start|>system\\n' + messages[0]['content'] + '<|im_end|>\\n' }}{%- else -%}{{- '<|im_start|>system\\nYou are a helpful assistant.<|im_end|>\\n' }}{%- endif -%}{%- for message in messages -%}{%- if message.role == 'system' and loop.first -%}{# Skip #}{%- else -%}{{- '<|im_start|>' + message['role'] + '\\n' + message['content'] + '<|im_end|>' + '\\n' }}{%- endif -%}{%- endfor -%}{%- if add_generation_prompt -%}{{- '<|im_start|>assistant\\n' }}{%- endif -%}",
+  "bos_token": "<|im_start|>",
+  "chat_template": "{%- if messages[0]['role'] == 'system' -%}{{- '<|im_start|>system\\n' + messages[0]['content'] + '<|im_end|>\\n' }}{%- else -%}{{- '<|im_start|>system\\nYou are a helpful assistant.<|im_end|>\\n' }}{%- endif -%}{%- for message in messages -%}{%- if message.role == 'system' and loop.first -%}{# Skip #}{%- else -%}{{- '<|im_start|>' + message['role'] + '\\n' + message['content'] + '<|im_end|>' + '\\n' }}{%- endif -%}{%- endfor -%}{%- if add_generation_prompt -%}{{- '<|im_start|>assistant\\n' }}{%- if enable_thinking is defined and enable_thinking is true -%}{{- '<think>\\n' }}{%- endif -%}{%- endif -%}",
   "clean_up_tokenization_spaces": false,
   "eos_token": "<|im_end|>",
   "extra_special_tokens": {},
@@ -169,4 +169,4 @@
   "tokenizer_class": "GPT2Tokenizer",
   "unk_token": "<|endoftext|>",
   "vocab_size": 49152
-}
+}