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/XChaCha20Poly1305CompatTests.swift

@@ -13,7 +13,7 @@ import struct Foundation.Data
 struct XChaCha20Poly1305CompatTests {
 
     @Test func sealAndOpenRoundtrip() throws {
-        let plaintext = "Hello, XChaCha20-Poly1305!".data(using: .utf8)!
+        let plaintext = Data("Hello, XChaCha20-Poly1305!".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let nonce = Data(repeating: 0x24, count: 24)
 
@@ -29,10 +29,10 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealAndOpenWithAAD() throws {
-        let plaintext = "Secret message".data(using: .utf8)!
+        let plaintext = Data("Secret message".utf8)
         let key = Data(repeating: 0xAB, count: 32)
         let nonce = Data(repeating: 0xCD, count: 24)
-        let aad = "additional authenticated data".data(using: .utf8)!
+        let aad = Data("additional authenticated data".utf8)
 
         let sealed = try XChaCha20Poly1305Compat.seal(plaintext: plaintext, key: key, nonce24: nonce, aad: aad)
         let decrypted = try XChaCha20Poly1305Compat.open(
@@ -47,7 +47,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealProducesDifferentCiphertextWithDifferentNonces() throws {
-        let plaintext = "Same plaintext".data(using: .utf8)!
+        let plaintext = Data("Same plaintext".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let nonce1 = Data(repeating: 0x01, count: 24)
         let nonce2 = Data(repeating: 0x02, count: 24)
@@ -59,7 +59,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnShortKey() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let shortKey = Data(repeating: 0x42, count: 16)
         let nonce = Data(repeating: 0x24, count: 24)
 
@@ -73,7 +73,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnLongKey() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let longKey = Data(repeating: 0x42, count: 64)
         let nonce = Data(repeating: 0x24, count: 24)
 
@@ -87,7 +87,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnEmptyKey() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let emptyKey = Data()
         let nonce = Data(repeating: 0x24, count: 24)
 
@@ -116,7 +116,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnShortNonce() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let shortNonce = Data(repeating: 0x24, count: 12)
 
@@ -130,7 +130,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnLongNonce() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let longNonce = Data(repeating: 0x24, count: 32)
 
@@ -144,7 +144,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func sealThrowsOnEmptyNonce() {
-        let plaintext = "Test".data(using: .utf8)!
+        let plaintext = Data("Test".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let emptyNonce = Data()
 
@@ -173,7 +173,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func openFailsWithWrongKey() throws {
-        let plaintext = "Secret".data(using: .utf8)!
+        let plaintext = Data("Secret".utf8)
         let correctKey = Data(repeating: 0x42, count: 32)
         let wrongKey = Data(repeating: 0x43, count: 32)
         let nonce = Data(repeating: 0x24, count: 24)
@@ -195,7 +195,7 @@ struct XChaCha20Poly1305CompatTests {
     }
 
     @Test func openFailsWithTamperedCiphertext() throws {
-        let plaintext = "Secret".data(using: .utf8)!
+        let plaintext = Data("Secret".utf8)
         let key = Data(repeating: 0x42, count: 32)
         let nonce = Data(repeating: 0x24, count: 24)