Yet more flinitfy (and related tweaks)

[fingolfin]

Also remove redundant jacobi_symbol method.

[codecov]

Codecov Report

Attention: Patch coverage is 76.23762% with 24 lines in your changes missing coverage. Please review.

Project coverage is 87.30%. Comparing base (fbef9d1) to head (a97503b).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/antic/nf_elem.jl	8.33%	11 Missing ⚠️
src/flint/fmpq_poly.jl	0.00%	7 Missing ⚠️
src/arb/Complex.jl	80.00%	2 Missing ⚠️
src/flint/fmpz_mat.jl	93.75%	2 Missing ⚠️
src/flint/fmpz.jl	83.33%	1 Missing ⚠️
src/flint/fmpz_poly.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1876      +/-   ##
==========================================
- Coverage   87.34%   87.30%   -0.04%     
==========================================
  Files          97       97              
  Lines       35832    35745      -87     
==========================================
- Hits        31297    31207      -90     
- Misses       4535     4538       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[fingolfin]

test coverage for adhoc operations is really bad. Would be good to have more of those in the interface tests (possibly optionally, as I am not sure we mandate this in the ring interface?)

[lgoettgens]

the ring interface states that it is optional to add explicit ad-hoc functions, but AA should take care of the fallback using promotion (see https://nemocas.github.io/AbstractAlgebra.jl/dev/ring_interface/#Optional-binary-ad-hoc-operators)

[lgoettgens]

the matrix constructor changes are very hard to follow. maybe the next time put moving and changing into two different commit? Anyway, I don't see anything bad standing out