refactor: simplify PlatformLog actuals and convert remaining interpolated log calls to lambdas

- Extract private log() helper in JVM and iOS PlatformLog to reduce
  copy-paste branching
- Fix JVM formatter to be private and non-nullable
- Convert 60+ interpolated Log.w/e/i calls to lambda overloads,
  including hot-path Filter.kt toJson() and LocalCache event processing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/robohash/RobohashAssembler.kt

@@ -167,7 +167,7 @@ class RobohashAssembler {
             if (Hex.isHex(msg) && msg.length > 10) {
                 Hex.decode(msg)
             } else {
-                Log.w("Robohash", "$msg is not a hex")
+                Log.w("Robohash") { "$msg is not a hex" }
                 sha256(msg.toByteArray())
             }