fix: bind setTimeout to globalThis in SupabaseBroadcastAdapter for browser compatibility (#402)

# Fix setTimeout context binding issue in SupabaseBroadcastAdapter

This PR fixes a browser compatibility issue in the `SupabaseBroadcastAdapter` class where `setTimeout` was losing its context binding when used in browser environments. The issue would cause an error: `"'setTimeout' called on an object that does not implement interface Window"`.

The fix:
- Properly binds `setTimeout` to the global context using `setTimeout.bind(globalThis)` in the constructor
- Adds comprehensive tests to verify the fix works correctly

This issue only manifested in browser environments, not in Node.js, which explains why our existing tests didn't catch it. I've added a test that simulates the browser's strict context requirements for `setTimeout`.

The PR also includes a planning document for implementing browser-based testing to catch similar issues in the future.

Author: jumski

.changeset/fix-settimeout-binding.md

@@ -0,0 +1,5 @@
+---
+'@pgflow/client': patch
+---
+
+Fix setTimeout context binding issue in SupabaseBroadcastAdapter for browser compatibility

pkgs/client/src/lib/SupabaseBroadcastAdapter.ts

@@ -42,7 +42,7 @@ export class SupabaseBroadcastAdapter implements IFlowRealtime {
     this.#supabase = supabase;
     this.#reconnectionDelay = opts.reconnectDelayMs ?? 2000;
     this.#stabilizationDelay = opts.stabilizationDelayMs ?? 300;
-    this.#schedule = opts.schedule ?? setTimeout;
+    this.#schedule = opts.schedule ?? setTimeout.bind(globalThis);
   }
 
   /**