feat: add test for local search with PatternPerturbation

tests: add test for Linear fitness function

refactor: extend local search to accept any inputs

Instead of accepting only BinaryString, accept anything.
Extend the operators to accept anything.

tests: move all tests to separate submodules

tests: add rosenbrock test

chore: guard test imports by #[cfg(test)]

chore: split types and functions to separate module files