Fix: correct regex for file-preview URL re-signing (#25620)

Fixes #25619

The regex patterns for file-preview and image-preview contained an unescaped `?`, 
which caused incorrect matches such as `file-previe` or `image-previw`. 
This led to malformed URLs being incorrectly re-signed.

Changes:
- Escape `?` in both file-preview and image-preview regex patterns.
- Ensure only valid URLs are re-signed.

Added unit tests to cover:
- Valid file-preview and image-preview URLs (correctly re-signed).
- Misspelled file/image preview URLs (no longer incorrectly matched).

Other:
- Fix a deprecated function `datetime.utcnow()`

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Asuka Minato <i@asukaminato.eu.org>
Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

api/models/model.py

@@ -1044,7 +1044,7 @@ class Message(Base):
                 sign_url = sign_tool_file(tool_file_id=tool_file_id, extension=extension)
             elif "file-preview" in url:
                 # get upload file id
-                upload_file_id_pattern = r"\/files\/([\w-]+)\/file-preview?\?timestamp="
+                upload_file_id_pattern = r"\/files\/([\w-]+)\/file-preview\?timestamp="
                 result = re.search(upload_file_id_pattern, url)
                 if not result:
                     continue
@@ -1055,7 +1055,7 @@ class Message(Base):
                 sign_url = file_helpers.get_signed_file_url(upload_file_id)
             elif "image-preview" in url:
                 # image-preview is deprecated, use file-preview instead
-                upload_file_id_pattern = r"\/files\/([\w-]+)\/image-preview?\?timestamp="
+                upload_file_id_pattern = r"\/files\/([\w-]+)\/image-preview\?timestamp="
                 result = re.search(upload_file_id_pattern, url)
                 if not result:
                     continue