docs: backfill changelog entries for the #2312-#2407 range (#2412)

Problem: of the 60 pull requests merged in the #2312-#2407 range, only
#2334, #2336, #2337, #2340 and #2348 wrote a 1.5.0 changelog entry, and
#2398 and #2403 only reworded lines that were already there. Every other
user-visible change in the range -- wire-semantics fixes, maker guards,
reassembly behaviour, public-API and error-message changes -- went
unrecorded, so the entry no longer describes the release.

Fix: one entry per user-visible pull request, in each module section's
existing style and ordered by the issue it closes. Three pairs share a
bullet, since each is the direct follow-up or counterpart of the other:
#2393 with #2401, #2405 with #2407, and #2392 with #2403. The diff on the
entry file is purely additive.

Internal-only work is left out deliberately: dependency and action bumps
(#2387 to #2391), test-only and docs-prose passes (#2333, #2376, #2379,
#2380, #2402), the unreachable-branch removal (#2378), and the #: comment
marker the HIP Group and Packet crawlers now write (#2381). That last one
renders nothing either way: the marker lands inside the generated
_missing_ body, conf.py's exclude-members drops _missing_ from autodoc,
and a comment in a method body is not an attribute comment to begin with.

#2392 and #2403 are recorded together, under Added rather than Fixed, for
the declarations they introduce: __proto_key__ on each class owning a
__proto__ registry (#2392), __proto_dest__ on the enum registries and
Vendor.PROTO_DEST to generate it (#2403). The bullet names those classes
and registries rather than counting them, per the no-counted-numbers rule
for the unreleased entry. Both PRs added the autodoc entries, so both are
rendered public attributes. #2392's rejection-message
change is deliberately not recorded as a fix: the bare "code must be ..."
text it prefixed came from _check_code, which #2193 introduced and which
is in no release tag -- absent at v1.5.0b14 -- so no released version ever
emitted it. #2403 is no longer skipped as internal because it reworded an
existing bullet to name __proto_dest__ while nothing credited the
attribute's introduction.

Four claims are corrected against the source rather than carried over:
FTP_DATA shipped in pcapkit/protocols/application/ftp.py from 1.0.0, not
1.4.0 (class FTP_DATA(Raw) is there at v1.0.0); #2365's pre-fix fallback
read cmmd.value, so a .value-carrying object was accepted unchecked
rather than raising; #2399 left the dpkt adapter and the adapters'
ModuleNotFound raises alone, so it claims no universal prefix; and
#2397's old tail did name the version it got, so the entry quotes it and
gains the :issue:`2302` it was missing. #2370's "a Section Header Block
... still fails" sentence is dropped: #2369 settles the byte order first,
and an SHB built from raw octets with ctx=None now rebuilds byte-exact in
both byte orders.

CHANGELOG.md is regenerated with util/changelog_md.py.

Test: tests/project/ in full, 0 failures, including test_changelog_md.py's
in-step and supported-subset checks; util/changelog_md.py --check reports
the two files in step; the entry parses under docutils with no structural
warning.

Author: JarryShaw