refactor(rust/sedona-spatial-join): Unify execute and execute_knn, move end-to-end tests in exec.rs to tests directory#593

Kontinuation merged 2 commits intoapache:mainapache/sedona-db:mainfrom

Kontinuation:unify-execute-and-execute-knnKontinuation/sedona-db:unify-execute-and-execute-knnCopy head branch name to clipboard