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/Integration/IntegrationTests.swift

@@ -174,7 +174,7 @@ struct IntegrationTests {
             }
             
             // Encrypted path: use NoiseSessionManager explicitly
-            let plaintext = "Encrypted message".data(using: .utf8)!
+            let plaintext = Data("Encrypted message".utf8)
             let ciphertext = try helper.noiseManagers["Alice"]!.encrypt(plaintext, for: helper.nodes["Bob"]!.peerID)
             
             helper.nodes["Bob"]!.packetDeliveryHandler = { packet in
@@ -206,7 +206,7 @@ struct IntegrationTests {
         
         try await confirmation("Messages delivered despite churn", expectedCount: totalMessages) { completion in
             // David tracks received messages
-            helper.nodes["David"]!.messageDeliveryHandler = { message in
+            helper.nodes["David"]!.messageDeliveryHandler = { _ in
                 completion()
             }
             
@@ -288,7 +288,7 @@ struct IntegrationTests {
             }
             
             do {
-                let plaintext = "After restart success".data(using: .utf8)!
+                let plaintext = Data("After restart success".utf8)
                 let ciphertext = try helper.noiseManagers["Bob"]!.encrypt(plaintext, for: helper.nodes["Alice"]!.peerID)
                 let packet = TestHelpers.createTestPacket(type: MessageType.noiseEncrypted.rawValue, payload: ciphertext)
                 helper.nodes["Alice"]!.packetDeliveryHandler = { pkt in

bitchatTests/Integration/TestNetworkHelper.swift

@@ -121,4 +121,3 @@ final class TestNetworkHelper {
         _ = try manager2.handleIncomingHandshake(from: peer1ID, message: msg3)
     }
 }
-