refactor: run natively on node type stripping, modernize tooling

Replaces enums with erasable const modules (inlined by esbuild via
minifySyntax), adds explicit .ts import extensions, and drops
mocha/c8/mocha-snap/tsx in favor of node:test with built-in coverage.
Updates all dependencies to latest, including eslint 10 flat config
and TypeScript 6.

Author: DylanPiercey

.c8rc.json

@@ -0,0 +1,5 @@
+---
+"htmljs-parser": minor
+---
+
+Replace TypeScript enums with erasable const modules so the source runs directly under node's type stripping. The public `TagType`, `ErrorCode`, and `Validity` values keep their runtime shape and values, and their types are now the equivalent literal unions. Constant values remain fully inlined in the published bundles.

.changeset/shiny-llamas-search.md

@@ -34,7 +34,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest]
-        node: [20, 22, 24]
+        node: [22, 24, 26]
     steps:
       - name: Checkout code
         uses: actions/checkout@v6

.eslintignore

@@ -15,5 +15,5 @@ dist
 *.tsbuildinfo
 
 # Coverage
-.nyc_output
 coverage
+lcov.info

.eslintrc.json

@@ -1,5 +1,4 @@
 {
   "*.ts": ["eslint --fix", "prettier --write"],
-  "*{.js,.json,.md,.yml,rc}": ["prettier --write"],
-  "./package.json": ["fixpack"]
+  "*{.js,.json,.md,.yml,rc}": ["prettier --write"]
 }