0.8.0: pretty logger (Log) + crash capture

- Log: static entry + scoped Loggers (Log.tag), six levels, lazy messages,
  structured fields, ANSI ConsoleSink, DeveloperSink, MemorySink, NoopSink.
  Sinks compose via +; throwing sinks are isolated.
- Log.configure wires FlutterError/PlatformDispatcher/isolate errors through
  Log.e by default; log-then-rethrow deduped via Expando.
- UxKeyboard: migrate kDebugMode print() to Log.tag('KB').d lazily.
- Depend on package:clock for testable timestamps.

example/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -5,6 +5,8 @@
 import FlutterMacOS
 import Foundation
 
+import ux
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  UxPlugin.register(with: registry.registrar(forPlugin: "UxPlugin"))
 }