fix: recognise inline verbatim opening after an attached modifier

[docker-run]

Problem

_`Tree`_ is parsed by tree-sitter-norg as (underline (verbatim)), but this parser returns the backticks as plain Special tokens, so the verbatim is lost:

_`Tree`_   =>  AttachedModifier { '_', content: [Special('`'), Text("Tree"), Special('`')] }

With more than one verbatim inside a modifier the result is worse than a dropped node — the pairing shifts:

_`a` and `b`_  =>  [Special('`'), Text("a"), InlineVerbatim([Whitespace, Text("and"), Whitespace]), Text("b"), Special('`')]

and becomes the verbatim, and a/b do not.

Cause

Both attached-modifier opener candidates end with

.then(just(ParagraphSegmentToken::Whitespace).not())

which expresses "must not be followed by whitespace" but consumes the token it tests. When that token is a backtick, the opener swallows it and inline_verbatim never sees an opening delimiter. The swallowed token is then re-emitted as a plain Token by unravel_candidates, which is why it surfaces as Special('')`.

Fix

Peek instead of consuming — but only for `, so every other parse path is byte-identical:

let opener_rhs = || {
    choice((
        just(ParagraphSegmentToken::Special(VERBATIM)).rewind(),
        just(ParagraphSegmentToken::Whitespace).not(),
    ))
};

and unravel_candidates skips re-emitting the token it no longer consumed.

Rewinding unconditionally also fixes verbatim, but regresses */hello/*, world!: left_empty_opening_modifier stops consuming its right token, and / is then re-claimed as a new opener's left context, so the whole paragraph degrades to bare tokens. Hence the narrow condition.

Result

_`Tree`_       =>  AttachedModifier { '_', content: [InlineVerbatim([Text("Tree")])] }
_`a *b* c`_    =>  content stays raw: [Text("a"), Whitespace, Special('*'), Text("b"), ...]
_`a` and `b`_  =>  [InlineVerbatim([Text("a")]), Whitespace, Text("and"), Whitespace, InlineVerbatim([Text("b")])]

All matching tree-sitter-norg.

Tests

Existing suite passes unchanged (34/34, no snapshot updates). Adds verbatim_after_attached_modifier covering verbatim directly after a modifier, multiple verbatims in one modifier, raw content inside a nested verbatim, and the previously-working cases as regression guards.

Found while building a Norg editor on this crate, where the same case silently dropped formatting on read.