Fix missing TypeScript declarations in published package (#850)

* fix: add explicit RegExp type annotations to restore TypeScript declaration generation

UNICODE_PUNCT_R and UNICODE_WHITESPACE_R were exported vars without explicit
type annotations. @bunup/dts uses oxc-transform's isolatedDeclaration() to
generate .d.ts files, which requires all exported bindings to have explicit
types. Without them, TS9010 errors are emitted. In CI (isCI=true), these
errors are fatal and cause process.exit(1) before any .d.ts files are
written — which is why published packages v9.7.10 and v9.7.11 were missing
their type declarations entirely.

Closes #849

* chore: add changeset for type declarations fix

Author: stevenocchipinti

.changeset/fix-missing-type-declarations.md

@@ -0,0 +1,5 @@
+---
+'markdown-to-jsx': patch
+---
+
+Fix missing TypeScript declaration files in published package.

lib/src/utils.ts

@@ -464,8 +464,8 @@ export function isASCIIWhitespace(code: number): boolean {
 // Per GFM spec Section 2.1: "A punctuation character is a character in the general Unicode categories
 // Pc, Pd, Pe, Pf, Pi, Po, or Ps" - this is \p{P}
 // BUT also includes some currency symbols and other symbols per the spec's explicit list
-export var UNICODE_PUNCT_R = /[\p{P}\p{S}]/u
-export var UNICODE_WHITESPACE_R = /\p{Zs}/u
+export var UNICODE_PUNCT_R: RegExp = /[\p{P}\p{S}]/u
+export var UNICODE_WHITESPACE_R: RegExp = /\p{Zs}/u
 
 export function isUnicodeWhitespace(c: string): boolean {
   if (!c) return true