Add support for \mbox conversion to text and update tests

[AndPuQing]

[qwinsi]

Sorry but I think this feature has better way to implement.
To implement it please have a look on:

• how \operatorname{XXX} is tokenized in tex-tokenizer.ts
• how \operatorname{XXX} is converted in convert.ts

Or I will consider this work once I have time in the feature.

[AndPuQing]

The LaTeX \mbox{} command needs to preserve its content as literal text in Typst, but unlike \operatorname{} or \text{}, it can contain nested LaTeX commands:

• \mbox{mc}
• \mbox{\textrm{a}}

The standard approach used for other commands: String.raw\\(text|operatorname|...){(.+?)}

This regex uses non-greedy matching (.+?) which stops at the first closing brace:

• Input: \mbox{\textrm{a}}
• Regex captures: \textrm{a (stops at first })
• Remaining: } (unmatched, causes parse error)

I use manual brace counting in the tokenizer:

1. Match \mbox{ with regex
2. Scan character-by-character, maintaining a brace counter
3. Increment on {, decrement on }
4. Stop when counter reaches 0 (found matching brace)

This correctly handles: \mbox{\textrm{a}} → captures \textrm{a} as LITERAL

In convert.ts, I check for \mbox before calling convert_tex_node_to_typst(node.args[0]) because:

• The LITERAL token contains raw LaTeX like \textrm{a}
• The converter doesn't recognize \textrm{a} as a valid token (it's meant to stay as literal text)
• We access the raw content directly and escape backslashes for Typst strings

Result: \mbox{\textrm{a}} → "\textrm{a}" (Typst text with escaped backslash)

[qwinsi]

So the support for this feature is quite challenging.

Letting it alone until an enhancement is applied on the tex parser in the future. (e.g. LatexParser should have a member vairable such as this.envronment: "literal" | "math")