server : (refactor) no more json in server_task input (#10691)

* server : (refactor) no more json in server_task input

* add test for slots endpoint

* add tests for /props and /slots

* remove task inf_type

* fix CI by adding safe_json_to_str

* add "model_path" to /props

* update readme

Author: ngxson

Diff for: examples/server/README.md

@@ -687,12 +687,14 @@ This endpoint is public (no API key check). By default, it is read-only. To make
     }
   },
   "total_slots": 1,
+  "model_path": "../models/Meta-Llama-3.1-8B-Instruct-Q4_K_M.gguf",
   "chat_template": "..."
 }
 ```
 
 - `default_generation_settings` - the default generation settings for the `/completion` endpoint, which has the same fields as the `generation_settings` response object from the `/completion` endpoint.
 - `total_slots` - the total number of slots for process requests (defined by `--parallel` option)
+- `model_path` - the path to model file (same with `-m` argument)
 - `chat_template` - the model's original Jinja2 prompt template
 
 ### POST `/props`: Change server global properties.