fix: clone tx status objects in legacy polling to prevent shared reference bug

The legacy polling actor's SUBSCRIBE handler sends ctx.all() (its internal
KVS object) by reference, and the POLL handler mutates it via ctx.merge().
When the new createObservable wrapper (introduced in #2258) stores this
reference as `value` and later compares with isDiff(), the deepEqual check
short-circuits on `a === b` (same object reference) and always returns
false — so status updates are never delivered to subscribers.

Fix: spread the objects before sending/broadcasting so consumers get
their own copy.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jribbink

packages/fcl-core/src/transaction/legacy-polling.js

@@ -56,7 +56,7 @@ const makeHandlers = (opts = {}) => ({
   },
   [SUBSCRIBE]: (ctx, letter) => {
     ctx.subscribe(letter.from)
-    ctx.send(letter.from, UPDATED, ctx.all())
+    ctx.send(letter.from, UPDATED, {...ctx.all()})
   },
   [UNSUBSCRIBE]: (ctx, letter) => {
     ctx.unsubscribe(letter.from)
@@ -96,7 +96,7 @@ const makeHandlers = (opts = {}) => ({
     }
 
     if (!isSealed(tx)) poll()
-    if (isDiff(prevTx, tx)) ctx.broadcast(UPDATED, tx)
+    if (isDiff(prevTx, tx)) ctx.broadcast(UPDATED, {...tx})
     ctx.merge(tx)
   },
 })