Simplify Tensor struct

[mofeing]

Closes #89

[jofrevalles]

Everything looks good to me!

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (49d32d9) 80.29% compared to head (dac9c68) 80.41%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
+ Coverage   80.29%   80.41%   +0.11%     
==========================================
  Files          14       14              
  Lines         934      909      -25     
==========================================
- Hits          750      731      -19     
+ Misses        184      178       -6     

Files	Coverage Δ
ext/TenetChainRulesCoreExt.jl	86.36% <100.00%> (ø)
ext/TenetMakieExt.jl	100.00% <100.00%> (ø)
ext/TenetQuacExt.jl	86.95% <100.00%> (ø)
src/Quantum/MP.jl	90.00% <100.00%> (+0.86%)	⬆️
src/Quantum/Quantum.jl	74.19% <ø> (+0.45%)	⬆️
src/Tenet.jl	100.00% <ø> (ø)
src/Tensor.jl	88.99% <100.00%> (+0.01%)	⬆️
src/Transformations.jl	97.50% <100.00%> (ø)
src/Quantum/PEP.jl	0.00% <0.00%> (ø)
src/Numerics.jl	88.70% <33.33%> (ø)

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[mofeing]

Funk, this PR is more merging in master.