feat: Adding system solvers to the Flutter example

[albertodev01]

Why?

Currently, the web example is missing a page for system solving algorithms so it's time to add it!

What?

I have added the systems page inside example/flutter_example and written unit/widget/golden tests

Types of Changes

• New feature (non-breaking change which adds functionality)
• Documentation change (change to update documentation)

Notes

I have also made some minor format changes to the equations package and added a named constructor to initialize systems from a flattened matrix.

Checklist

• I have provided a description of the proposed changes.
• I added unit tests for all relevant code.
• I added golden tests for all UI changes.
• I added documentation for all relevant code.

[codecov-commenter]

Codecov Report

Merging #23 (780b4cd) into master (89e5a0d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #23   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           50        50           
  Lines         1816      1844   +28     
=========================================
+ Hits          1816      1844   +28     

Impacted Files	Coverage Δ
lib/src/system/system.dart	100.00% <100.00%> (ø)
lib/src/system/types/cholesky.dart	100.00% <100.00%> (ø)
lib/src/system/types/gauss.dart	100.00% <100.00%> (ø)
lib/src/system/types/gauss_seidel.dart	100.00% <100.00%> (ø)
lib/src/system/types/jacobi.dart	100.00% <100.00%> (ø)
lib/src/system/types/lu.dart	100.00% <100.00%> (ø)
lib/src/system/types/sor.dart	100.00% <100.00%> (ø)

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