🐛 Bug [flutter_link_previewer]: URL with underscore _ is truncated

[khoidv-dipro]

Description
flutter_link_previewer fails to detect full URLs when the path or query contains underscore (_).
Example: YouTube Live URLs are truncated during parsing.
This causes incorrect preview data and broken link previews in production apps.

Steps to reproduce

1. Use LinkPreview with the following text:
   https://www.youtube.com/live/wFTD_Tm9als?si=w99NseYI2KIDz7_Z
2. Observe the detected link in onLinkPreviewDataFetched

Actual behavior
The detected URL is truncated:
https://www.youtube.com/live/wFTD_

Expected behavior
The full URL should be detected:
https://www.youtube.com/live/wFTD_Tm9als?si=w99NseYI2KIDz7_Z

Root cause
The internal regex used to detect links does not allow underscore (_) in the final path/query segment.