fix: harden Turtle movement block parser with bounds checks

The Turtle parseMovementBlock had no bounds checking on any reads.
Since Packet::readUInt8() returns 0 past the end without failing, the
parser could "succeed" with all-zero garbage data, then subsequent
parseUpdateFields would read from wrong positions, producing
"truncated field value" and "truncated update mask" errors.

Added bounds checks before every conditional read section (transport,
swimming pitch, fall time, jumping, spline elevation, speeds, spline
data, tail flags). Also removed the WotLK movement block fallback from
the Turtle parser chain — WotLK format is fundamentally incompatible
(uint16 flags, 9 speeds) and false-positive parses corrupt NPC data.
Also changed spline pointCount > 256 from cap-to-zero to return false
so the parser correctly fails instead of silently dropping waypoints.

src/game/world_packets.cpp

@@ -1024,7 +1024,7 @@ bool UpdateObjectParser::parseMovementBlock(network::Packet& packet, UpdateBlock
             /*float splineElevation =*/ packet.readFloat();
         }
 
-        // Speeds (7 speed values)
+        // Speeds (9 values in WotLK: walk/run/runBack/swim/swimBack/flight/flightBack/turn/pitch)
         /*float walkSpeed =*/ packet.readFloat();
         float runSpeed = packet.readFloat();
         /*float runBackSpeed =*/ packet.readFloat();