Implement DualMatrix to be able to solve 2nd order problems

[max-vassili3v]

This PR provides a minimal implementation of DualMatrix so that we are able to do 2nd order differentiation (as shown by the example in the unit tests) by allowing DualVectors with a DualVector value and a DualMatrix jacobian, thus being able to create 'nested dual arrays'. That can propagate higher order derivatives. We have:

• Constructor for DualMatrix
• Basic indexing of DualMatrices
• Some bug fixes surrounding promotion
• Remove unnecessary project dependencies

Next steps:

• Make DualMatrix fully functional and behave as expected with existing types (DualMatrix-DualVector multiplication, reshape, etc.)
• Look into dependencies that can help with sparse/efficient tensor calculations (SparseArrayKit.jl, TensorOperations.jl)

[codecov]

Codecov Report

❌ Patch coverage is 78.37838% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.87%. Comparing base (5761344) to head (374f054).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/types.jl	68.42%	6 Missing ⚠️
src/arithmetic.jl	75.00%	1 Missing ⚠️
src/utilities.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #26      +/-   ##
==========================================
+ Coverage   70.87%   71.87%   +1.00%     
==========================================
  Files           5        5              
  Lines         103      128      +25     
==========================================
+ Hits           73       92      +19     
- Misses         30       36       +6     

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