Implement Hardware I/O Simulator (OUT/INP/WAIT/MOTOR, port emulation)

New portio.c module following the virmem.c dispatch-by-address pattern,
emulating 8253 PIT channel 2 (speaker frequency), PPI port B (speaker
on/off), CGA mode/color select registers, game port (joystick stub),
COM1 serial (transmitter-ready stub), and floating bus default (0xFF).

OUT/WAIT/MOTOR statements and INP()/STICK()/STRIG() functions now fully
functional. Continuous tone generation via PulseAudio pthread worker for
programs that drive the speaker through OUT &H43/&H42/&H61.

tests/expected/portio.expected

@@ -0,0 +1,9 @@
+INP(0)= 255
+INP(&H201)= 240
+COM1 LSR= 96
+PPI= 0
+CGA MODE= 0
+MOTOR OK
+STICK(0)= 128
+STRIG(0)= 0
+DONE

tests/expected/speaker_out.expected

@@ -0,0 +1 @@
+SPEAKER OK