feat: add custom CEF V8 extensions support (#17)

* feat: Register extensions in render process

- Add CefExtensions type to hold V8 extension code
- Pass extensions through BrowserProcessAppBuilder
- Register extensions in RenderProcessHandler on WebKit initialization
- Decode JSON extensions from command line switch
- Prefix extension names with "v8/" per CEF convention
- Include actual JSON in error messages for debugging

l

* feat: refactor window.cef API and register as CEF extension

* fix: remove debug print statements in render process handler

* refactor: centralize EXTENSIONS_SWITCH constant in util.rs

* fmt

* refactor: implement Default trait for CefApiHandler

* docs: add documentation for CefApiHandler and its JavaScript API functions

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Co-authored-by: not-elm <elmgameinfo@gmail.com>

assets/host_emit.html

@@ -15,7 +15,7 @@
 <h1 id="count" style="color: aqua">0</h1>
 <script>
     const count = document.getElementById("count");
-    window.cef.listen("count", (payload) => {
+    cef.listen("count", (payload) => {
         count.innerText = payload;
     })
 </script>