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 :warning:

Additional details and impacted files

```diff @@ 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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