adapt to GradedArrays v0.4

[ogauthe]

This PR adapts FusionTensors to GradedArrays 'v0.4'. All tests are now passing. The next step is to define FusionTensorAxes.

[codecov]

Codecov Report

Attention: Patch coverage is 90.47619% with 6 lines in your changes missing coverage. Please review.

Project coverage is 90.41%. Comparing base (d891cbb) to head (6867690).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fusiontensor/base_interface.jl	37.50%	5 Missing ⚠️
src/fusion_trees/fusiontree.jl	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   90.03%   90.41%   +0.37%     
==========================================
  Files          10       10              
  Lines         532      532              
==========================================
+ Hits          479      481       +2     
+ Misses         53       51       -2     

Flag	Coverage Δ
docs	0.00% <0.00%> (ø)

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[mtfishman]

Looks good, nice to see this updated.