feat: add configurable write_stdin timeout (#12228)

Add max timeout as config for `write_stdin`. This is only used for empty
`write_stdin`.

Also increased the default value from 30s to 5mins.

codex-rs/core/config.schema.json

@@ -1295,6 +1295,12 @@
       "default": null,
       "description": "Settings for app-specific controls."
     },
+    "background_terminal_timeout": {
+      "description": "Maximum poll window for background terminal output (`write_stdin`), in milliseconds. Default: `300000` (5 minutes).",
+      "format": "uint64",
+      "minimum": 0.0,
+      "type": "integer"
+    },
     "chatgpt_base_url": {
       "description": "Base URL for requests to ChatGPT (as opposed to the OpenAI API).",
       "type": "string"