feat: add timestamp to output filenames for cache-busting

Add get_timestamp() and format_output_filename() utilities to folder_paths.py
that generate unique filenames with UTC timestamps. This eliminates the need
for client-side cache-busting query parameters.

New filename format: prefix_00001_20260131-220945-123456_.ext

Updated all save nodes to use the new format:
- nodes.py (SaveImage, SaveLatent, SaveImageWebsocket)
- comfy_api/latest/_ui.py (UILatent)
- comfy_extras/nodes_video.py (SaveWEBM, SaveAnimatedPNG, SaveAnimatedWEBP)
- comfy_extras/nodes_images.py (SaveSVG)
- comfy_extras/nodes_hunyuan3d.py (Save3D)
- comfy_extras/nodes_model_merging.py (SaveCheckpointSimple)
- comfy_extras/nodes_lora_extract.py (LoraSave)
- comfy_extras/nodes_train.py (SaveEmbedding)

Amp-Thread-ID: https://ampcode.com/threads/T-019c17e5-1c0a-736f-970d-e411aae222fc

folder_paths.py

@@ -4,6 +4,7 @@ import os
 import time
 import mimetypes
 import logging
+from datetime import datetime, timezone
 from typing import Literal, List
 from collections.abc import Collection
 
@@ -11,6 +12,46 @@ from comfy.cli_args import args
 
 supported_pt_extensions: set[str] = {'.ckpt', '.pt', '.pt2', '.bin', '.pth', '.safetensors', '.pkl', '.sft'}
 
+
+def get_timestamp() -> str:
+    """Generate a filesystem-safe timestamp string for output filenames.
+
+    Returns a UTC timestamp in the format YYYYMMDD-HHMMSS-ffffff (microseconds)
+    which is human-readable, lexicographically sortable, and Windows-safe.
+    """
+    now = datetime.now(timezone.utc)
+    return now.strftime("%Y%m%d-%H%M%S-%f")
+
+
+def format_output_filename(
+    filename: str,
+    counter: int,
+    ext: str,
+    *,
+    batch_num: str | None = None,
+    timestamp: str | None = None,
+) -> str:
+    """Format an output filename with counter and timestamp for cache-busting.
+
+    Args:
+        filename: The base filename prefix
+        counter: The numeric counter for uniqueness
+        ext: The file extension (with or without leading dot)
+        batch_num: Optional batch number to replace %batch_num% placeholder
+        timestamp: Optional timestamp string (defaults to current UTC time)
+
+    Returns:
+        Formatted filename like: filename_00001_20260131-123456-789012_.ext
+    """
+    ext = ext.lstrip(".")
+    if timestamp is None:
+        timestamp = get_timestamp()
+
+    if batch_num is not None:
+        filename = filename.replace("%batch_num%", batch_num)
+
+    return f"{filename}_{counter:05}_{timestamp}_.{ext}"
+
 folder_names_and_paths: dict[str, tuple[list[str], set[str]]] = {}
 
 # --base-directory - Resets all default paths configured in folder_paths with a new base path