feat(combat): support self targeted and area skills

feat(game): handle null skill vnum in su packet responder

fix(game): create character on at packet received

fix(game): make effects vnum short instead of long

fix(combat): do not return successfully when walk position is equal to target position

fix(packets): add header for st sub packet

chore: bump versions to support new PacketSerializer

chore: update Game

chore: fix workflow to work with .net 7

chore: update PacketSerializer version

fix(packets): add missing usings

feat(packets): do not add the same packet multiple times

chore: move PacketSerializer types to correct namespace

feat(packets): add support for st buff vnums with levels

Merge pull request #32 from Rutherther/combat

Add combat extension

chore: update versions

feat(combat): remove item selector from simple attack technique

feat(tests): add Ski packet test

fix(game): create npc instead of monster in InResponder

chore(data): add cast time and cooldown units to documentation