chore: Adding more tests and fixing minor issues

[albertodev01]

Why?

I need to add more tests to the library to make it more robust and improve the eigenvalues algorithm.

Right now, to compute eigenvalues the library uses a not-so-stable algorithm. It just iterates the product or R x Q of the QR decomposition and returns items in the diagonal. This is correct but it's numerically unstable so we need Householder reflections and improvements

What?

• I have implemented the EigenDecomposition<K, T extends Matrix<K>> type
• Now rank() and eigenvalues() work correctly

Types of Changes

• Bug fix (non-breaking change which fixes an issue)

Notes

This PR also includes the new 'Integrals' page of the Flutter example app (located at example/flutter_example).

There also is a BREAKING CHANGE since NumericalIntegration now requires the function via constructor (earlier it was passed to the integrate() function)

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 #26 (a2a209a) into master (c888118) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master       #26    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           65        66     +1     
  Lines         2850      2975   +125     
==========================================
+ Hits          2850      2975   +125     

Impacted Files	Coverage Δ
lib/src/algebraic/types/quadratic.dart	100.00% <ø> (ø)
.../src/interpolation/types/newton_interpolation.dart	100.00% <ø> (ø)
lib/src/system/types/gauss.dart	100.00% <ø> (ø)
...sitions/singular_value_decomposition/real_svd.dart	100.00% <ø> (ø)
lib/src/utils/math_utils.dart	100.00% <ø> (ø)
lib/src/algebraic/algebraic.dart	100.00% <100.00%> (ø)
lib/src/algebraic/types/durand_kerner.dart	100.00% <100.00%> (ø)
lib/src/algebraic/utils/algebraic_division.dart	100.00% <100.00%> (ø)
.../src/algebraic/utils/polynomial_long_division.dart	100.00% <100.00%> (ø)
lib/src/algebraic/utils/sylvester_matrix.dart	100.00% <100.00%> (ø)
... and 30 more

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