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/Performance/PerformanceBaselineTests.swift

@@ -301,7 +301,7 @@ final class PerformanceBaselineTests: XCTestCase {
             ("@carol#a1b2 did you see this? https://example.com/threads/42", ["carol"]),
             ("checking in from the harbor #bitchat #mesh", nil),
             ("@bob#0042 ping me when you get this", ["bob#0042"]),
-            ("long form update with a link https://news.example.org/articles/2026/06/mesh-networks and a tag #geohash", nil),
+            ("long form update with a link https://news.example.org/articles/2026/06/mesh-networks and a tag #geohash", nil)
         ]
         let batches: [[BitchatMessage]] = (0..<batchCount).map { batch in
             (0..<batchSize).map { i in
@@ -547,7 +547,7 @@ final class PerformanceBaselineTests: XCTestCase {
             "anyone near the station?",
             "@bob#0042 are you on mesh too?",
             "check this out https://example.com/p/123 #bitchat",
-            "teleport check, who's local?",
+            "teleport check, who's local?"
         ]
         return try (0..<count).map { i in
             try NostrProtocol.createEphemeralGeohashEvent(