Fix simple IO bugs

[craigthomas]

This PR fixes three simple IO bugs. First, the SYNC instruction was hanging the emulator due to the fact that the CPU was put into a suspended state, without any ability to trigger any additional interrupts. Second, video modes should not be updated when the SAM control registers are updated - only when the data register for the VDG is written to should the video mode be updated. Finally, it was possible to write into the ROM address space through the IO mapped memory segment of $FF00 - $FFFF. This PR fixes these specific IO bugs.

[codecov]

Codecov Report

Attention: Patch coverage is 27.27273% with 8 lines in your changes missing coverage. Please review.

Project coverage is 57.39%. Comparing base (e22e9cd) to head (1f434cc).

Files with missing lines	Patch %	Lines
...a/ca/craigthomas/yacoco3e/components/Emulator.java	0.00%	4 Missing ⚠️
.../craigthomas/yacoco3e/components/IOController.java	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #130      +/-   ##
============================================
- Coverage     57.40%   57.39%   -0.02%     
+ Complexity     1028     1027       -1     
============================================
  Files            68       68              
  Lines          4562     4556       -6     
  Branches        514      514              
============================================
- Hits           2619     2615       -4     
+ Misses         1859     1857       -2     
  Partials         84       84              

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