Better handling of (N)FFT operators for different NFFT backends

[nHackel]

• Re-adds fftParams to NFFTOperator
• Specialises fft parameter for backend and array type combinations
• Adds NonuniformFFTs as second backend to test
• With LinearOperatorCollection 2.2.1, this should mean MRIOperators is compatible with NonuniformFFTSs

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.87%. Comparing base (5a0faa5) to head (365639c).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...IOperatorsGPUArraysExt/MRIOperatorsGPUArraysExt.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #264   +/-   ##
=======================================
  Coverage   74.86%   74.87%           
=======================================
  Files         102      103    +1     
  Lines        5415     5420    +5     
=======================================
+ Hits         4054     4058    +4     
- Misses       1361     1362    +1     

Flag	Coverage Δ
MRIBase	50.19% <ø> (ø)
MRICoilSensitivities	93.07% <ø> (ø)
MRIFiles	78.59% <ø> (ø)
MRIOperators	40.18% <42.85%> (-0.01%)	⬇️
MRIReco	42.23% <57.14%> (-0.01%)	⬇️
MRISampling	0.35% <ø> (ø)
MRISimulation	63.07% <ø> (ø)

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