CVE-2026-53530: ratex-parser panics on `\verb` with a multibyte delimiter (UTF-8 byte-boundary slice)

The public parser entrypoint ratex_parser::parse(&str) panics on the 9-byte input \verbéxé (i.e. \verb followed by the non-ASCII delimiter é). When handling a \verb command, the parser slices the verbatim argument with byte indices (arg[1..arg.len() - 1]); if the delimiter character is multibyte UTF-8, index 1 lands inside that character and Rust panics with “byte index 1 is not a char boundary”. Because RaTeX’s release profile sets panic = "abort" (Cargo.toml:48), the panic aborts the entire process — not just the current request/thread — making this a hard denial of service for any service that renders untrusted LaTeX.