optimise hot-path audio pipeline: zero-copy ring buffer, pre-allocated converter buffers

- Replace Swift Array<UInt8> ring buffer with UnsafeMutableRawPointer to
  eliminate COW ref-count checks on every write/read
- Add append(from:count:) to copy directly from Core Audio buffer pointer
  into the ring buffer, removing the per-callback Data heap allocation
- Pre-allocate AVAudioPCMBuffer pair in AudioFormatConverter and reuse
  across transform() calls (lazy init, capacity-checked)
- Fix float-to-int truncation in output frame count calculation (ceil)
- Add comprehensive AudioBuffer test suite (12 tests) including proper
  wrap-around coverage for both append and read paths

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

Sources/AudioTeeCore/Core/AudioTapManager.swift

@@ -8,7 +8,7 @@ public class AudioTapManager {
   private var deviceID: AudioObjectID?
 
   public init() {}
-  
+
   deinit {
     AudioTeeLogging.logger.debug("Cleaning up audio tap manager")
 
@@ -76,7 +76,8 @@ public class AudioTapManager {
     AudioTeeLogging.logger.debug(
       "AudioHardwareCreateProcessTap completed", context: ["status": String(status)])
     guard status == kAudioHardwareNoError else {
-      AudioTeeLogging.logger.error("Failed to create audio tap", context: ["status": String(status)])
+      AudioTeeLogging.logger.error(
+        "Failed to create audio tap", context: ["status": String(status)])
       throw AudioTeeError.tapCreationFailed(status)
     }
 
@@ -115,7 +116,8 @@ public class AudioTapManager {
     let status = AudioHardwareCreateAggregateDevice(description as CFDictionary, &deviceID)
 
     guard status == kAudioHardwareNoError else {
-      AudioTeeLogging.logger.error("Failed to create aggregate device", context: ["status": String(status)])
+      AudioTeeLogging.logger.error(
+        "Failed to create aggregate device", context: ["status": String(status)])
       throw AudioTeeError.aggregateDeviceCreationFailed(status)
     }