improve tensor printing

[dsyme]

Show tensors as

tensor([[.... data ]],dtype=Float32,device=cuda:2,backend=Torch)

suppressing the extra information if the values are the current system defaults

[codecov]

Codecov Report

Merging #234 into dev will increase coverage by 5.53%.
The diff coverage is 68.00%.

@@            Coverage Diff             @@
##              dev     #234      +/-   ##
==========================================
+ Coverage   67.02%   72.55%   +5.53%     
==========================================
  Files          18       18              
  Lines        5279     5734     +455     
  Branches     1305     1329      +24     
==========================================
+ Hits         3538     4160     +622     
+ Misses       1024      835     -189     
- Partials      717      739      +22     

Impacted Files	Coverage Δ
src/DiffSharp.Core/Device.fs	25.00% <0.00%> (+19.74%)	⬆️
src/DiffSharp.Core/Tensor.fs	78.09% <40.00%> (+8.36%)	⬆️
src/DiffSharp.Core/RawTensor.fs	84.62% <76.47%> (-2.79%)	⬇️
src/DiffSharp.Core/Backend.fs	78.57% <100.00%> (+4.21%)	⬆️
src/DiffSharp.Core/Dtype.fs	55.10% <100.00%> (+22.54%)	⬆️
src/DiffSharp.Core/DiffSharp.Numerical.fs	77.63% <0.00%> (-3.95%)	⬇️
src/DiffSharp.Backends.Torch/Torch.RawTensor.fs	85.81% <0.00%> (-0.05%)	⬇️
src/DiffSharp.Core/Util.fs	55.56% <0.00%> (+0.24%)	⬆️
src/DiffSharp.Core/Data.fs	74.67% <0.00%> (+0.69%)	⬆️
... and 12 more