feat: Added Riddler's method and updated Flutter example

[albertodev01]

Why?

I need to update the Flutter example in example/flutter_example and add a new root finding algorithm to the core library

What?

I've added the new Riddler type and updated the Flutter example.

Types of Changes

• New feature (non-breaking change which adds functionality)
• General improvements (quality updates to improve the stability of the project)

Notes

The Flutter example app is being worked on the flutter_example branch!

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 #29 (c0af23f) into master (ba95fc3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #29   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           66        67    +1     
  Lines         2973      3004   +31     
=========================================
+ Hits          2973      3004   +31     

Impacted Files	Coverage Δ
lib/src/algebraic/types/durand_kerner.dart	100.00% <ø> (ø)
.../src/interpolation/types/newton_interpolation.dart	100.00% <ø> (ø)
lib/src/nonlinear/nonlinear.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/bisection.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/brent.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/chords.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/newton.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/regula_falsi.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/secant.dart	100.00% <ø> (ø)
lib/src/nonlinear/types/steffensen.dart	100.00% <ø> (ø)
... and 3 more

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