Add Brent's method for minimization

[nossleinad]

This pull request implements Brent's method for minimization and calls it brents_method_minimize. It also makes it an option as an optimizer for branchlength_optim!. This method can be used for 1D unimodal optimization problems and it doesn't use derivatives.

Additionally, this pull request generalizes golden_section_maximize and brents_method_minimize with univariate_maximize. It dispatches on the two different subtypes, GoldenSectionOptand BrentsMethodOpt, of the new UnivariateOpt-type.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.36066% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 32.99%. Comparing base (6930e8d) to head (3abdcf3).

Files	Patch %	Lines
src/core/algorithms/branchlength_optim.jl	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #15      +/-   ##
==========================================
+ Coverage   31.23%   32.99%   +1.76%     
==========================================
  Files          30       30              
  Lines        2126     2182      +56     
==========================================
+ Hits          664      720      +56     
  Misses       1462     1462              

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