Speed up is_homogeneous

[fingolfin]

Some measurements taking the example from the is_homogeneous docstring:

R, (x, y, z) = graded_polynomial_ring(QQ, ["x", "y", "z"], [1, 2, 3])
f = x^2+y*z
W = [1 2 1 0; 3 4 0 1]
S, (w, x, y, z) = graded_polynomial_ring(QQ, ["w", "x", "y", "z"], W)
F = w^3*y^3*z^3 + w^2*x*y^2*z^2 + w*x^2*y*z + x^3

Before:

julia> @btime is_homogeneous(f);
  1.533 μs (62 allocations: 2.28 KiB)

julia> @btime is_homogeneous(F);
  3.932 μs (152 allocations: 5.53 KiB)

After:

julia> @btime is_homogeneous(f);
  334.071 ns (10 allocations: 416 bytes)

julia> @btime is_homogeneous(F);
  556.150 ns (12 allocations: 656 bytes)

I will make a separate PR for Hecke which provides addmul!, zero! and more for FinGenAbGroupElem.

Also I think there are more places that could be similarly improved, e.g. homogeneous_components. However, unlike is_homogeneous they did not stick out in some timing profiles on CI tests we made this week.

[HechtiDerLachs]

If it works, it works. Thanks!

[joschmitt]

I now get 10 respectively 12 allocations in the example.

[lgoettgens]

Maybe we wait for a release of thofma/Hecke.jl#1619 and then can simplify the comments away?

[fingolfin]

But that then also needs to go into a new Hecke release, and then more benchmarking should be done to verify it doesn't get slower again etc. I'd rather have this in fact sooner. IMHO the "simplification" is not as important as the speed up.

[lgoettgens]

Alright. Then let's get this in

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.66%. Comparing base (33595be) to head (269bab0).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4119   +/-   ##
=======================================
  Coverage   84.65%   84.66%           
=======================================
  Files         626      626           
  Lines       84313    84316    +3     
=======================================
+ Hits        71377    71382    +5     
+ Misses      12936    12934    -2     

Files with missing lines	Coverage Δ
src/Rings/mpoly-graded.jl	91.47% <100.00%> (+0.02%)	⬆️

... and 2 files with indirect coverage changes

[lgoettgens]

Hecke 0.34.3 is now released with the required changes.

[lgoettgens]

I now adapted to the new Hecke functions, and verified that this does not increase the allocations nor the runtime of the example above.

@fingolfin if you are happy with this, please merge