fix(packets): correctly use cast id instead of vnum in UseSkill packet

Revert "feat(packets): make position ushort"

This reverts commit 8610668d17586fc8d502d8c86842af9504729c7a.

feat(packets): make position ushort

Merge pull request #8 from Rutherther/game-objects

Game objects

fix: implement IPacket in use skill packets

feat: split packets definitions into separate assembly