Riemann tensor on product manifold

[mateuszbaran]

@kellertuer second PR with Riemann tensor 🙂

[codecov]

Codecov Report

Merging #543 (97a851c) into master (8250a6f) will increase coverage by 59.41%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master     #543       +/-   ##
===========================================
+ Coverage   39.52%   98.94%   +59.41%     
===========================================
  Files         100      100               
  Lines        9507     9659      +152     
===========================================
+ Hits         3758     9557     +5799     
+ Misses       5749      102     -5647     

Impacted Files	Coverage Δ
src/manifolds/ProductManifold.jl	96.31% <100.00%> (+51.43%)	⬆️
src/tests/tests_group.jl	95.01% <0.00%> (-0.24%)	⬇️
src/nlsolve.jl	100.00% <0.00%> (+11.11%)	⬆️
src/manifolds/GeneralUnitaryMatrices.jl	100.00% <0.00%> (+15.48%)	⬆️
src/tests/tests_general.jl	96.90% <0.00%> (+22.31%)	⬆️
src/Manifolds.jl	100.00% <0.00%> (+23.07%)	⬆️
src/distributions.jl	88.88% <0.00%> (+38.88%)	⬆️
src/utils.jl	100.00% <0.00%> (+39.83%)	⬆️
src/product_representations.jl	96.70% <0.00%> (+47.25%)	⬆️
src/cotangent_space.jl	88.23% <0.00%> (+50.00%)	⬆️
... and 66 more

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[kellertuer]

Nice, thanks for the quick PR :)