refactor: add prompt_id as hidden type, fix imports, add docstrings

- Add PROMPT_ID as a new hidden type in the Hidden enum, HiddenHolder,
  HiddenInputTypeDict, and execution engine resolution (both V3 and legacy)
- Refactor GetImageSize to use cls.hidden.prompt_id instead of manually
  calling get_executing_context() — addresses reviewer feedback
- Remove lazy import of get_executing_context from nodes_images.py
- Add docstrings to send_progress_text, _display_text, HiddenHolder,
  and HiddenHolder.from_dict

Amp-Thread-ID: https://ampcode.com/threads/T-019ca1cb-0150-7549-8b1b-6713060d3408

comfy_api_nodes/util/client.py

@@ -437,6 +437,17 @@ def _display_text(
     status: str | int | None = None,
     price: float | None = None,
 ) -> None:
+    """Send a progress text message to the client for display on a node.
+
+    Assembles status, price, and text lines, then sends them via WebSocket.
+    Automatically retrieves the current prompt_id from the execution context.
+
+    Args:
+        node_cls: The ComfyNode class sending the progress text.
+        text: Optional text content to display.
+        status: Optional status string or code to display.
+        price: Optional price in dollars to display as credits.
+    """
     display_lines: list[str] = []
     if status:
         display_lines.append(f"Status: {status.capitalize() if isinstance(status, str) else status}")