mh/mod ZZMatrix ZZRingElem

[fingolfin]

• Improve mod and mod! for ZZMatrix plus ZZRingElem
• Move some more things out of HeckeMoreStuff.jl

[codecov]

Codecov Report

Attention: Patch coverage is 21.56863% with 40 lines in your changes missing coverage. Please review.

Project coverage is 87.91%. Comparing base (d12b72e) to head (1285f7a).

Files with missing lines	Patch %	Lines
src/flint/fmpz_mat.jl	0.00%	13 Missing ⚠️
src/antic/nf_elem.jl	33.33%	12 Missing ⚠️
src/flint/fmpz_mod.jl	0.00%	12 Missing ⚠️
src/flint/fmpz.jl	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1982      +/-   ##
==========================================
- Coverage   87.94%   87.91%   -0.04%     
==========================================
  Files          98       98              
  Lines       36072    36076       +4     
==========================================
- Hits        31725    31717       -8     
- Misses       4347     4359      +12     

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