fix: Fix catastrophic backtracking (ReDoS) in link/reflink label regex (#3918)

Co-authored-by: UziTech <97994+UziTech@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

src/rules.ts

@@ -373,7 +373,7 @@ const tag = edit(
   .replace('attribute', /\s+[a-zA-Z:_][\w.:-]*(?:\s*=\s*"[^"]*"|\s*=\s*'[^']*'|\s*=\s*[^\s"'=<>`]+)?/)
   .getRegex();
 
-const _inlineLabel = /(?:\[(?:\\[\s\S]|[^\[\]\\])*\]|\\[\s\S]|`+[^`]*?`+(?!`)|[^\[\]\\`])*?/;
+const _inlineLabel = /(?:\[(?:\\[\s\S]|[^\[\]\\])*\]|\\[\s\S]|`+(?!`)[^`]*?`+(?!`)|``+(?=\])|[^\[\]\\`])*?/;
 
 const link = edit(/^!?\[(label)\]\(\s*(href)(?:(?:[ \t]+(?:\n[ \t]*)?|\n[ \t]*)(title))?\s*\)/)
   .replace('label', _inlineLabel)

test/specs/redos/backticks_in_link_no_close.html

@@ -0,0 +1 @@
+<p>[<code>code0</code> <code>code1</code> <code>code2</code> <code>code3</code> <code>code4</code> <code>code5</code> <code>code6</code> <code>code7</code> <code>code8</code> <code>code9</code> <code>code10</code> <code>code11</code> <code>code12</code> <code>code13</code> <code>code14</code></p>

test/specs/redos/backticks_in_link_no_close.md

@@ -0,0 +1 @@
+[````code0```` ````code1```` ````code2```` ````code3```` ````code4```` ````code5```` ````code6```` ````code7```` ````code8```` ````code9```` ````code10```` ````code11```` ````code12```` ````code13```` ````code14````