fix(ipv6): a CALIPSO option loses its trailing pad and shrinks its length on rebuild #1403

Describe the bug
A CALIPSO option whose Opt Data Len exceeds 8 + 4×cmpt_len loses its trailing pad on rebuild, and the option length drops with it. The pad is read into a PaddingField sized by calipso_pad_len (pcapkit/protocols/schema/internet/hopopt.py:473, ipv6_opts.py:473). The data class has no field for it, and make never emits it. The RFC 5570 checksum covers that pad.

To Reproduce

• HOPOPT.from_data(HOPOPT(raw).info) turns 3b01 070c 00000001 00 05 0000 00000000 into 3b01 0708 00000001 00 05 0000 01020000: the length goes from 12 to 8, and a PadN replaces the pad.
• A non-zero pad gives the same output.

Expected behavior
The option length and pad survive byte-exact.

Reproduced on main at 79949ec3d and found by the PaddingField sweep. Related: #1223, #1232.