Fix array prop update edge cases

[brentyi]

This snippet was hitting edge cases in both the server and client logic:

import trimesh.creation
import viser

icosphere = trimesh.creation.icosphere(subdivisions=3, radius=1.0)

server = viser.ViserServer()
serializer = server.get_scene_serializer()

sphere_handle = server.scene.add_mesh_simple(
    "/mesh", vertices=icosphere.vertices, faces=icosphere.faces
)

for i in range(100):
    icosphere.vertices *= 1.05
    sphere_handle.vertices = icosphere.vertices
    serializer.insert_sleep(1.0 / 5.0)

serializer.show()