add WVTT (WebVTT in MP4) subtitle converter for subby (#61)

* chore(deps): update subby to 0.3.27

* fix(subs): add WVTT (WebVTT in MP4) subtitle converter for subby

- Use WVTTConverter if self.codec == Subtitle.Codec.fVTT
- Read or save files as Paths instead of strings to avoid AttributeErrors
- Add CommonIssuesFixer when stripping SDH
- Set Subtitle.Codec.fVTT to use subby if conversion_method == "auto"
- Silence the underlying srt library logging used by subby to avoid info messages being printed to console

pyproject.toml

@@ -120,4 +120,4 @@ no_implicit_optional = true
 
 [tool.uv.sources]
 unshackle = { workspace = true }
-subby = { git = "https://github.com/vevv/subby.git", rev = "5a925c367ffb3f5e53fd114ae222d3be1fdff35d" }
+subby = { git = "https://github.com/vevv/subby.git", rev = "1ea6a52028c5bea8177c8abc91716d74e4d097e1" }