Add .opus to audio source extension detection

[reasonset]

Current Behavior:

If a source file has the .opus extension, it cannot be identified as an audio file.
If a HEAD request to the server returns audio/ogg, the file can be played back as audio as a fallback; however, if the implementation incorrectly returns audio/opus, an error will occur.

Expected Behavior:

If the URL has the .opus extension, it should be identified as audio.

Steps To Reproduce:

1. Specify a URL with the .opus extension in Vidstack's src

repro: https://codeberg.org/reasonset-tiny/repro-vidstack-opus-extension-issue

Environment:

• Framework: Vanilla
• Meta Framework: None
• Node: None
• Device: Vivaldi, Librewolf, Cromite, Waterfox
• OS: Linux, ColorOS16

Anything Else?

[reasonset]

I also noticed a related issue while testing this: .ogg is currently included in VIDEO_EXTENSIONS, so Ogg Vorbis files with the conventional .ogg extension are detected as video sources.
.ogv should be video, while .ogg is conventionally used for Ogg Vorbis audio (and .oga for generic Ogg audio).
This probably belongs to the same extension detection table, but I can open a separate issue if preferred.