Keep original utility implementations, only use jsonfile
Removed es-toolkit dependency and reverted to the original custom implementations for pick, omit, groupBy, and partition utilities. These are simple, well-tested functions that don't need external dependencies. Kept only jsonfile (3.5KB) for JSON file I/O as it handles edge cases properly.
Co-authored-by: fisker <172584+fisker@users.noreply.github.com>
