Unsafe ops for ZZRingElem, QQFieldElem

[fingolfin]

Move flintify calls down into unsafe ops

Also reorder method defs to add,sub,mul

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 12 lines in your changes missing coverage. Please review.

Project coverage is 87.24%. Comparing base (1e48bb0) to head (9a55fbf).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/flint/fmpz.jl	56.25%	7 Missing ⚠️
src/flint/fmpq.jl	82.14%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1905      +/-   ##
==========================================
- Coverage   87.25%   87.24%   -0.02%     
==========================================
  Files          97       97              
  Lines       35651    35651              
==========================================
- Hits        31109    31103       -6     
- Misses       4542     4548       +6     

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