Burn down SwiftLint advisory violations from 109 to 4 (#1362)

Mechanical style fixes across the enabled rule set, mostly via
swiftlint --fix (trailing_comma, comma, colon, trailing_newline,
comment_spacing, unused_closure_parameter, unneeded_break_in_switch,
opening_brace) plus hand fixes:

- non_optional_string_data_conversion (45): .data(using: .utf8)! and
  ?? Data() fallbacks replaced with the non-optional Data(_.utf8),
  including two production sites (NIP-44 HKDF info constant and the
  announce canonicalization context/nickname bytes — byte-identical
  output, only the impossible-nil handling is gone).
- switch_case_alignment: LocationChannel had a misindented closing
  brace; also repaired an --fix artifact in BLEService's .none case.
- redundant_string_enum_value: TrustLevel raw values equal to the case
  names (encoded form unchanged).
- unused_optional_binding: let _ = binds replaced with != nil / is Bool.
- static_over_final_class: PreviewView.layerClass.
- Resolved the BinaryProtocolTests TODO by documenting that 8-byte
  recipient ID truncation is the fixed wire-field size, not a bug.

The 4 remaining violations are all todo markers for a shared
test-helpers module (tracked in #1088) and one Reuse note.

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/ChatLifecycleCoordinatorContextTests.swift

@@ -214,10 +214,10 @@ struct ChatLifecycleCoordinatorContextTests {
         // Same message under both keys: the read copy must win over sent.
         context.privateChats[peerID] = [
             makePrivateMessage(id: "m1", timestamp: t1, deliveryStatus: .sent),
-            makePrivateMessage(id: "m2", timestamp: t2),
+            makePrivateMessage(id: "m2", timestamp: t2)
         ]
         context.privateChats[stablePeerID] = [
-            makePrivateMessage(id: "m1", timestamp: t1, deliveryStatus: .read(by: "alice", at: t2)),
+            makePrivateMessage(id: "m1", timestamp: t1, deliveryStatus: .read(by: "alice", at: t2))
         ]
 
         let merged = coordinator.getPrivateChatMessages(for: peerID)
@@ -245,7 +245,7 @@ struct ChatLifecycleCoordinatorContextTests {
             makePrivateMessage(id: "m1", senderPeerID: convKey),
             makePrivateMessage(id: "already-acked", senderPeerID: convKey),
             makePrivateMessage(id: "relay", senderPeerID: convKey, isRelay: true),
-            makePrivateMessage(id: "mine", sender: "me", senderPeerID: context.myPeerID),
+            makePrivateMessage(id: "mine", sender: "me", senderPeerID: context.myPeerID)
         ]
 
         coordinator.markPrivateMessagesAsRead(from: convKey)
@@ -339,7 +339,7 @@ struct ChatLifecycleCoordinatorContextTests {
         )
         context.privateChats[peerID] = [
             makePrivateMessage(id: "in-1", senderPeerID: peerID),
-            makePrivateMessage(id: "in-relay", senderPeerID: peerID, isRelay: true),
+            makePrivateMessage(id: "in-relay", senderPeerID: peerID, isRelay: true)
         ]
 
         coordinator.markPrivateMessagesAsRead(from: peerID)