docs(changelog): seventh whole-repo pass over the changelog (#1103) (#2265)

- #876 item 3: state why the no-else-raise pragma stays, not "the belief"
- #652: the flagless HTTP/2 dump reads "Flags::0 [0]", as #648 renders it
- #2172: section_context raises only on a block holding no section
- add the missing #2222/#2232 MAC/EUI maker entry; cite #2257 on ARP
- add the #1055/#2244 engine-tests and required-checks entry that #849's
  and #856's job descriptions now need
- #800 names HTTP._guess_version, where the method lives; #631 states the
  old MANIFEST.in in the past tense
- drop mentions of never-released names (pcapkit.utilities.timestamp, a
  test constant)
- citation range runs to #2257; CHANGELOG.md regenerated

Author: JarryShaw