refactor: support symbolics v7

[oameye]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 56.82927% with 354 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.54%. Comparing base (af9d603) to head (b9b15b6).

Files with missing lines	Patch %	Lines
src/indexing.jl	50.00%	115 Missing ⚠️
src/index_average.jl	50.71%	103 Missing ⚠️
src/qnumber.jl	74.07%	42 Missing ⚠️
src/index_double_sums.jl	57.30%	38 Missing ⚠️
src/average.jl	52.00%	12 Missing ⚠️
src/index_utils.jl	69.23%	12 Missing ⚠️
src/printing.jl	0.00%	11 Missing ⚠️
src/cnumber.jl	33.33%	8 Missing ⚠️
src/utils.jl	80.00%	5 Missing ⚠️
src/spin.jl	0.00%	4 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
- Coverage   67.27%   65.54%   -1.73%     
==========================================
  Files          19       19              
  Lines        2454     2891     +437     
==========================================
+ Hits         1651     1895     +244     
- Misses        803      996     +193     

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