Add missing movement ACK responses to avoid server stalls

Implement generic handlers for force speed changes (walk, run back,
swim, swim back, flight, flight back, turn rate, pitch rate),
movement flag toggles (CAN_FLY, HOVER, feather fall, water walk),
and knockback ACKs. Fix SMSG_TIME_SYNC_REQ to respond with
CMSG_TIME_SYNC_RESP instead of silently dropping.

include/game/world_packets.hpp

@@ -399,6 +399,7 @@ enum class MovementFlags : uint32_t {
     ASCENDING           = 0x00400000,
     CAN_FLY             = 0x00800000,
     FLYING              = 0x01000000,
+    HOVER               = 0x02000000,
 };
 
 /**