core: move cross-spawn-spawner to root and remove unused types

The cross-spawn-spawner module has been moved from src/effect/ to src/
to simplify the core package structure. The src/types.d.ts file which
contained unused type declarations has also been removed. All imports
throughout the codebase have been updated to reflect the new location.

This change reduces the package's internal complexity by flattening the
module hierarchy and removing dead code, making future maintenance easier.