prohibit R reg from using CoreRegs::get

[6293]

No description provided.

[codecov]

Codecov Report

Merging #96 (941fef7) into master (f450cd2) will decrease coverage by 0.9%.
The diff coverage is 29.3%.

@@           Coverage Diff            @@
##           master     #96     +/-   ##
========================================
- Coverage    37.9%   37.0%   -0.9%     
========================================
  Files          20      22      +2     
  Lines        4861    5138    +277     
========================================
+ Hits         1842    1903     +61     
- Misses       3019    3235    +216     

Files Changed	Coverage Δ
src/data/arithm.rs	87.4% <ø> (+4.2%)	⬆️
src/data/bitwise.rs	57.4% <0.0%> (-35.6%)	⬇️
src/data/number.rs	47.9% <0.0%> (-0.7%)	⬇️
src/reg/families.rs	2.7% <0.0%> (-0.6%)	⬇️
src/data/byte_array.rs	25.9% <25.9%> (ø)
src/isa/exec.rs	45.3% <33.6%> (+0.7%)	⬆️
src/reg/core_regs.rs	66.6% <38.6%> (-1.2%)	⬇️
src/data/cmp.rs	54.2% <54.2%> (ø)
src/library/cursor.rs	100.0% <100.0%> (ø)
src/library/lib.rs	55.8% <100.0%> (ø)

... and 2 files with indirect coverage changes

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