Implement PSP audio playback via native sceAudio

Reserves a hardware channel per stream (64-aligned sample count,
mono/stereo format) and outputs through sceAudioOutputPannedBlocking,
giving PSP real stereo panning from directionality. Enforces the
44100Hz hardware-channel constraint with a clear error instead of
silently mispitching, and drops the shared test tone to 44100Hz to
match. Verified via the dusk-psp toolchain and a headless PPSSPP run
(correct channel reservation, onEnd firing once, no errors).

src/duskpsp/audio/CMakeLists.txt

@@ -0,0 +1,11 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+# Sources
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    audiopsp.c
+    audiostreampsp.c
+)