Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/collect-v8-coverage/index.js

@@ -0,0 +1,52 @@
+'use strict';
+
+const { Session } = require('inspector');
+const { promisify } = require('util');
+
+class CoverageInstrumenter {
+  constructor() {
+    this.session = new Session();
+
+    this.postSession = promisify(this.session.post.bind(this.session));
+  }
+
+  async startInstrumenting() {
+    this.session.connect();
+
+    await this.postSession('Profiler.enable');
+
+    await this.postSession('Profiler.startPreciseCoverage', {
+      callCount: true,
+      detailed: true,
+    });
+  }
+
+  async stopInstrumenting() {
+    const {result} = await this.postSession(
+      'Profiler.takePreciseCoverage',
+    );
+
+    await this.postSession('Profiler.stopPreciseCoverage');
+
+    await this.postSession('Profiler.disable');
+
+    // When using networked filesystems on Windows, v8 sometimes returns URLs
+    // of the form file:////<host>/path. These URLs are not well understood
+    // by NodeJS (see https://github.com/nodejs/node/issues/48530).
+    // We circumvent this issue here by fixing these URLs.
+    // FWIW, Python has special code to deal with URLs like this
+    // https://github.com/python/cpython/blob/bef1c8761e3b0dfc5708747bb646ad8b669cbd67/Lib/nturl2path.py#L22C1-L22C1
+    if (process.platform === 'win32') {
+      const prefix = 'file:////';
+      result.forEach(res => {
+        if (res.url.startsWith(prefix)) {
+          res.url = 'file://' + res.url.slice(prefix.length);
+        }
+      })
+    }
+
+    return result;
+  }
+}
+
+module.exports.CoverageInstrumenter = CoverageInstrumenter;