Tuning: Adjust default n_ctx from 512 to 2048

Author: riverzhou

llama_cpp/llama.py

@@ -17,7 +17,7 @@ def __init__(
         self,
         model_path: str,
         # NOTE: These parameters are likely to change in the future.
-        n_ctx: int = 512,
+        n_ctx: int = 2048,
         n_parts: int = -1,
         seed: int = 1337,
         f16_kv: bool = False,