Add ROM PAR mapping quirk to the MMU

[craigthomas]

This PR implements a ROM mapping quirk to the MMU. With ROM pages $3C to $3F, the mapping of the page to a task or executive PAR contains a quirk - the page requested uses the upper 6 bits from the page specified, but the bottom 2 bits from the slot that it is mapped into. This means that if page $3D is mapped to slot 2, the effective page mapped to slot 2 is $3E. Unit tests added to catch new conditions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.24%. Comparing base (5e83a86) to head (ff38c2f).
Report is 7 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #121      +/-   ##
============================================
- Coverage     54.90%   54.24%   -0.67%     
- Complexity      966      996      +30     
============================================
  Files            64       63       -1     
  Lines          4340     4515     +175     
  Branches        494      527      +33     
============================================
+ Hits           2383     2449      +66     
- Misses         1877     1982     +105     
- Partials         80       84       +4     

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