docs: #719-style prose sweep after the #1090–#1102 defect wave

Is your feature request related to a problem? Please describe.
The defect wave #1090–#1102 changes code and docstrings in several modules, and #719's two rounds of prose sweeps predate those changes. The maintainer asked for another #719-style pass over the docs and comments once the wave lands.

Describe the solution you'd like
Re-read the prose that the wave's merged PRs touched or made stale: docstrings, comments, docs/ and pep.rst. Apply #719's rules: no churn, accuracy first, no timed context, and only prose changes, with an AST guard on every .py.

Blocked until
Every issue in #1090–#1102 is closed.

Describe alternatives you've considered
Folding the sweep into each fix PR was rejected: thirteen parallel PRs editing shared prose would conflict.

Add to this sweep: ProtocolBase.pack() (protocol.py:559-576) rebuilds from make(**kwargs) and ignores the instance's parsed or constructed state. A bare X(...).pack() therefore returns defaults. Neither the docstring nor the rst docs say so. This came up in the #1143 review.

Add to this sweep, after #1147 merges:

docs/source/ext.rst:~266 says from_data "warns UnknownFieldWarning" and that its keywords "come from your _make_data". Caller-supplied keywords now raise UnsupportedCall.
The _check_construction_keywords docstring describes kwargs as what remains after __init__. from_data calls it as well now.

Still blocked, with a new condition. Every issue in #1090–#1102 is closed, but the sweep is meant to run after all the defects the wave turned up are fixed, so that it reads the final docstrings once. It now unblocks when #1127, #1133, #1144, #1151, #1154, #1155 and #1156 are all closed.

Still blocked, with a new condition. All seven issues named in the last condition are now closed. Two more defects from the same audit are now being fixed, #1165 and #1167, and they edit extraction.py, dumpkit/pcap.py, ipv4.py and udp.py. The sweep unblocks once #1165 and #1167 are both closed, so it reads the final docstrings once.

Condition extended: the #1169 cross-review turned up #1170, a defect in the same class that touches ipv4.py, ipv6.py, udp.py and the shared _import_next_layer. The sweep now unblocks once #1165, #1167 and #1170 are all closed.

The previous condition is met: #1165, #1167 and #1170 are all closed. Two defects from the same audit are still in flight: #1172 (l2tpv2.py) and #1173 (ipv6_route.py, mh.py, application.py). The sweep would read the docstrings of the files they edit, so it now unblocks when #1172 and #1173 are both closed. These are the last known items from this audit.

Unblocked: #1172 and #1173 are both closed (#1174 and #1176 merged at 04:00Z and 04:01Z). Now pending. Three later items are still open: #1175 (l2tpv2.py), #1177 (ipv6.py) and #1178 (ipv6_ext.py). The sweep skips those three files and they get a delta pass once each issue closes.

Dispatched as three prose slices, each scoped to git diff b10e7951b origin/main: protocols, schema-data and foundation-docs. The #1175/#1177/#1178 files are excluded.