fix(ipx): octets past the IPX Length field are dropped on rebuild #1433

Describe the bug
IPX behind Ethernet drops the octets past its Length field on rebuild, which is the IPX counterpart of #1209.

To Reproduce
A well-formed 30-octet IPX header (Length 30), with Ethernet type 0x8137, padded to a 60-octet frame: Ethernet.from_data(Ethernet(f).info).data gives 44 octets, not 60. It does this on main at a8cc02594 and on #1431's head.

Expected behavior
Byte-exact, per the every-round-trip ruling. Keep the excess as captured, the same way #1431 does for IPv4/IPv6 (info.trailer, written back after the packet, and not counted in Length).

Found while reviewing #1431. The fix belongs in pcapkit/protocols/{,schema/,data/}internet/ipx.py.