chore: vendor swabble and add speech usage strings

Swabble/Sources/SwabbleCore/Speech/BufferConverter.swift

@@ -0,0 +1,50 @@
+@preconcurrency import AVFoundation
+import Foundation
+
+final class BufferConverter {
+    private final class Box<T>: @unchecked Sendable { var value: T; init(_ value: T) { self.value = value } }
+    enum ConverterError: Swift.Error {
+        case failedToCreateConverter
+        case failedToCreateConversionBuffer
+        case conversionFailed(NSError?)
+    }
+
+    private var converter: AVAudioConverter?
+
+    func convert(_ buffer: AVAudioPCMBuffer, to format: AVAudioFormat) throws -> AVAudioPCMBuffer {
+        let inputFormat = buffer.format
+        if inputFormat == format {
+            return buffer
+        }
+        if converter == nil || converter?.outputFormat != format {
+            converter = AVAudioConverter(from: inputFormat, to: format)
+            converter?.primeMethod = .none
+        }
+        guard let converter else { throw ConverterError.failedToCreateConverter }
+
+        let sampleRateRatio = converter.outputFormat.sampleRate / converter.inputFormat.sampleRate
+        let scaledInputFrameLength = Double(buffer.frameLength) * sampleRateRatio
+        let frameCapacity = AVAudioFrameCount(scaledInputFrameLength.rounded(.up))
+        guard let conversionBuffer = AVAudioPCMBuffer(pcmFormat: converter.outputFormat, frameCapacity: frameCapacity)
+        else {
+            throw ConverterError.failedToCreateConversionBuffer
+        }
+
+        var nsError: NSError?
+        let consumed = Box(false)
+        let inputBuffer = buffer
+        let status = converter.convert(to: conversionBuffer, error: &nsError) { _, statusPtr in
+            if consumed.value {
+                statusPtr.pointee = .noDataNow
+                return nil
+            }
+            consumed.value = true
+            statusPtr.pointee = .haveData
+            return inputBuffer
+        }
+        if status == .error {
+            throw ConverterError.conversionFailed(nsError)
+        }
+        return conversionBuffer
+    }
+}