More mul!, addmul!, submul! methods for ZZRingElemOrPtr

[fingolfin]

Specifically, generalize some methods from ZZRingElem to ZZRingElemOrPtr,
and add missing variants for addmul! and submul!

[codecov]

Codecov Report

Attention: Patch coverage is 35.00000% with 13 lines in your changes missing coverage. Please review.

Project coverage is 86.44%. Comparing base (8ce122a) to head (ffb36b7).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/flint/fmpz.jl	35.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1860      +/-   ##
==========================================
- Coverage   86.46%   86.44%   -0.03%     
==========================================
  Files          98       98              
  Lines       36012    36021       +9     
==========================================
- Hits        31139    31137       -2     
- Misses       4873     4884      +11     

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[fingolfin]

My main criticism of this PR (that I made ;-) ) is that there are no tests for the new functions. Though there are also none for several of the existing methods ... :-/. I can add some when I find the time, or maybe someone else does, or maybe we just merge this for now if someone verifies that the ccalls look sane, and we add the tests later together with additional refactoring... ah well.

In the meantime I wonder what the HeckeCI error means, and if they are a fluke or in some way caused by this PR (but how?)

    ModAlgAss/Lattices/Lattices.jl          |    12           12
    LocalField/neq.jl                       |   252     2    254
    RCF/conductor_sieve.jl                  |    23           23
    FAILURE

The global RNG seed was 0xe1408e0caa2c92fc9de8b8de6ee5e7d6.

Error in testset LocalField/neq.jl:
Test Failed at /home/runner/.julia/packages/Hecke/dACt3/test/LocalField/neq.jl:57
  Expression: iszero(a) || valuation(a) > 20
Error in testset LocalField/neq.jl:
Test Failed at /home/runner/.julia/packages/Hecke/dACt3/test/LocalField/neq.jl:57
  Expression: iszero(a) || valuation(a) > 20
ERROR: LoadError: LoadError: Test run finished with errors
in expression starting at /home/runner/.julia/packages/Hecke/dACt3/test/parallel.jl:328
in expression starting at /home/runner/.julia/packages/Hecke/dACt3/test/runtests.jl:260
ERROR: Package Hecke errored during testing

[lgoettgens]

The HeckeCI error is thofma/Hecke.jl#1428

[fingolfin]

Then let's merge this and add the tests systematically a bit later