Track strikethrough (SGR 9) so it is not dropped across highlighted tokens

The `Attributes` ANSI style tracker in `src/vscreen.rs` declares, initializes,
clears (in `sgr_reset`), and re-emits (in `Display`) a `strike` field
documented as `ON: ^[9m / OFF: ^[29m`, but `update_with_sgr()` had no match
arm for SGR 9 (set strikethrough) or 29 (clear strikethrough). As a result
`strike` was only ever cleared, never set.

Because bat re-applies the tracked input ANSI style before each highlighted
text run (nu_ansi_term appends a full reset after every token), attributes
that are tracked — bold, dim, italic, underline — survive across tokens,
while strikethrough was silently dropped after the first token. This path is
active by default (`--strip-ansi`/`--sanitize` default to `never`).

Add the missing `9` and `29` arms, mirroring the sibling underline (4/24) and
italic (3/23) arms, so strikethrough is tracked and re-emitted like every
other supported attribute.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -25,6 +25,7 @@
 - Syntax highlighting for Python files using uv as script runner in shebang #3689 (@janlarres)
 
 ## Bugfixes
+- Track strikethrough (SGR 9 / 29) in the ANSI style tracker so it is re-emitted like bold, dim, italic, and underline, and is no longer dropped after the first highlighted token when displaying ANSI input with syntax highlighting, see #4015 (@mikehasa)
 - Allow boolean flags to be given more than once, so that a flag set in the config file can also be passed on the command line without erroring, see #3912 (@logarithmone1128)
 - Use parsed CLI arguments to detect number flags, see #3908 (@cuishuang)
 - Detect binary content beyond the first line, preventing encrypted files with early line breaks from being treated as text. Closes #3554, see #3877 (@Matei02355)