Time out tree-sitter CDN fetches to fix offline hang

Closes #51

When the network is fully offline, the <script src=cdn.jsdelivr.net>
tag for web-tree-sitter fails fast and TreeSitter is undefined, so
initTreeSitter() returns null immediately and analysis falls back to
the regex tokenizer. But on partially offline / flaky networks the
runtime script can load from cache while subsequent wasm fetches hang
indefinitely. TreeSitter.init() and Language.load() had no timeout,
so analysis stalled forever on "Loading language parsers...".

Wrap both calls in a Promise.race against an 8s timeout. A timeout
rejects into the existing catch block, which returns null and lets
the regex parser take over.

Author: Braedon Saunders

index.html

@@ -791,16 +791,23 @@
         lua:{grammar:'lua',exts:['.lua'],coverage:'available'},
         bash:{grammar:'bash',exts:['.sh','.bash','.zsh','.fish'],coverage:'available'}
     },
+    treeSitterFetchTimeoutMs:8000,
+    _withTimeout:function(promise,ms){
+        return Promise.race([
+            promise,
+            new Promise(function(_,reject){setTimeout(function(){reject(new Error('tree-sitter fetch timed out'));},ms);})
+        ]);
+    },
     initTreeSitter:async function(){
         if(this._tsRuntimePromise)return this._tsRuntimePromise;
         this._tsRuntimePromise=(async()=>{
             if(typeof TreeSitter==='undefined')return null;
             try{
-                await TreeSitter.init({
+                await Parser._withTimeout(TreeSitter.init({
                     locateFile:function(scriptName){
                         return 'https://cdn.jsdelivr.net/npm/web-tree-sitter@0.20.8/'+scriptName;
                     }
-                });
+                }),Parser.treeSitterFetchTimeoutMs);
                 return TreeSitter;
             }catch(e){
                 return null;
@@ -826,7 +833,7 @@
             var runtime=await Parser.initTreeSitter();
             if(!runtime)return null;
             try{
-                var lang=await runtime.Language.load(Parser.treeSitterWasmBase+'tree-sitter-'+config.grammar+'.wasm');
+                var lang=await Parser._withTimeout(runtime.Language.load(Parser.treeSitterWasmBase+'tree-sitter-'+config.grammar+'.wasm'),Parser.treeSitterFetchTimeoutMs);
                 var parser=new runtime();
                 parser.setLanguage(lang);
                 Parser._tsLanguages[config.grammar]=lang;