MilesLib: run the 40250 sound sources verbatim over an AIL software mixer

Copy SoundBase/SoundData/SoundInstance*/SoundManager*/Type from 40250 and
implement the AIL_* calls they make in MilesAil.cpp (2D pan, 3D distance and
listener pan, threaded stream decode, loop counts). The SDL host drains the
mixer. CSoundManager is created/updated/destroyed where 40250 does it and the
old AudioCommands bridge is removed. Port-map MilesLib 142/142 PORTED.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/port/common/Win32Crt.cpp

@@ -52,6 +52,11 @@ int _access(const char* path, int mode)
 	return access(path, m);
 }
 
+int _unlink(const char* path)
+{
+	return unlink(path);
+}
+
 namespace
 {
 struct FindState