fix(pcap): Header.pack() writes the same magic for every endian/nanosecond setting; _make_data returns magic_number #1125

Describe the bug

• Header(...).pack()[:4] is d4c3b2a1 for every combination of endian and nanosecond arguments, although .info.magic_number is correct. Seen by the fix(pcap): _make_magic ignores nanosecond with explicit endian flags; _read_protos ignores size #1112 reviewer, on both main and the PR.
• Header._make_data returns a magic_number key that make() does not declare, so from_data drops it with a warning. It is recorded in tests/protocols/test_construction_keyword_check_unit.py.

Blocked until
#1112 and #1115 merge. Both edit pcapkit/protocols/misc/pcap/header.py or its tests.

System information
main at bdba4fb9d, CPython 3.14.7, Linux.

Additional context
Found by the #1090–#1102 wave's audit and cross-reviews.