feat!: change crossover API & move crossover implementations into separate modules

[kkafar]

Description

• Set min. size of tournament to 1 in Tournament crossover op
• Move implementation of each crossover operator to separate module
• Remove unused imports
• Import warnings
• Update signature of crossover
• Fix tests in impls module
• Migrate UniformParameterized
• Migrate Uniform and update comments
• Migrate another few crossover impls
• Migrate rest of operators, examples & tests

This PR follows: kkafar/master-monorepo#236
See the link for full discussion on these changes.

Linked issues

Closes #470

Important implementation details

[kkafar]

Haven't checked whether all documentation comments do make sense after changes. <-- TODO