Add performance baselines; check dedup before verifying Nostr signatures

New PerformanceBaselineTests measure the hot paths (Nostr inbound, BLE
packet pipeline, GCS filters, delivery index, message formatting) with
deterministic fixtures and logged PERF metrics - baselines, not
assertions, so they cannot flake CI.

The suite immediately exposed that every inbound handler ran Schnorr
verification before the dedup lookup, so duplicate events - which
dominate real multi-relay traffic - each paid ~0.5ms of main-actor
crypto for nothing. All five handlers now do cheap rejects (kind, dedup
lookup) first and only record an event as processed AFTER its signature
verifies, so a forged-signature copy can never poison the dedup set and
suppress the genuine event. Gift-wrap verification also moves entirely
off the main actor with an atomic main-actor check-and-record.

Measured: duplicate-event handling 2.2k -> 1.39M events/sec (~640x);
fresh events unchanged (crypto-bound).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/ChatViewModelExtensionsTests.swift

@@ -411,11 +411,23 @@ struct ChatViewModelNostrExtensionTests {
         var invalidGiftWrap = giftWrap
         invalidGiftWrap.sig = String(repeating: "0", count: 128)
 
+        // Verification and recording now happen on a detached task; give the
+        // invalid copy time to be verified-and-rejected, then assert it never
+        // entered the dedup set.
         viewModel.handleNostrMessage(invalidGiftWrap)
+        try await Task.sleep(nanoseconds: 150_000_000)
         #expect(!viewModel.deduplicationService.hasProcessedNostrEvent(giftWrap.id))
 
         viewModel.handleNostrMessage(giftWrap)
-        #expect(viewModel.deduplicationService.hasProcessedNostrEvent(giftWrap.id))
+        var recorded = false
+        for _ in 0..<200 {
+            if viewModel.deduplicationService.hasProcessedNostrEvent(giftWrap.id) {
+                recorded = true
+                break
+            }
+            try await Task.sleep(nanoseconds: 10_000_000)
+        }
+        #expect(recorded)
     }
 
     @Test @MainActor