fix: increase stream-load-timeout to 6 seconds

@Asko-Dev reports that the `SteamLoadTimeoutError` seems to be thrown
"randomly" on iOS 17.5.1. That suggests that there is a race condition
with the timeout. Let's try to double the timeout (3s -> 6s) and see if
that helps.

See: #298

src/misc/camera.ts

@@ -84,8 +84,8 @@ async function runStartTask(
     // streams and never emit the `loadeddata` event. Looks like this is
     // related to a WebKit issue (see #298). No workarounds at the moment.
     // To at least detect this situation, we throw an error if the event
-    // has not been emitted after a 3 second timeout.
-    timeout(3000).then(() => {
+    // has not been emitted after a 6 second timeout.
+    timeout(6_000).then(() => {
       throw new StreamLoadTimeoutError()
     })
   ])

src/misc/errors.ts

@@ -27,7 +27,7 @@ export class InsecureContextError extends Error {
 export class StreamLoadTimeoutError extends Error {
   constructor() {
     super(
-      'Loading camera stream timed out after 3 seconds. If you are on iOS in PWA mode, this is a known issue (see https://github.com/gruhn/vue-qrcode-reader/issues/298)'
+      'Loading camera stream timed out after 6 seconds. If you are on iOS in PWA mode, this is a known issue (see https://github.com/gruhn/vue-qrcode-reader/issues/298)'
     )
 
     this.name = 'StreamLoadTimeoutError'