Add null byte as hard context separator

This allows one to use \0 as artificial separator, for example when concatting lots of small strings into a large string. See this discussion for context: https://github.com/orgs/meilisearch/discussions/744

charabia/src/separators.rs

@@ -64,6 +64,7 @@ pub const DEFAULT_SEPARATORS: &[&str] = &[
 
 #[rustfmt::skip]
 pub const CONTEXT_SEPARATORS: &[&str] = &[
+    "\0", // Null byte, can be used as artificial separator
     "᠆", // Mongolian Todo Soft Hyphen, mark the end of a paragraph.
     "᚛", "᚜", // Oghams, mark start and end of text
     "!", ". ", ", ", ";", "?", "¡", "§", "¶", "¿", ";", // Latin