milter, postfix, app, domain: cite the source of what they rely on (assumptions part B)

Comments only, no behaviour changed. go-milter v0.4.1 (session.go: one
session per connection, replaced after a non-continue reply; macros per
stage), Postfix 3.7.11 (milter8.c, smtpd_check.c
reject_auth_sender_login_mismatch(), mail_addr_find.c, showq_compat.c,
mail_conf_time.c, mail_params.h), Cyrus SASL 2.1.28 (saslpasswd.c,
plugins/sasldb.c: deleting a missing login is not an error), OpenDKIM
2.11.0~beta2 (opendkim-db.c, opendkim-genkey), Berkeley DB 5.3 db_dump,
rspamd 3.11.0. Comments that claimed what the source denies are corrected
(sasldb keeps the password as given, not hashed; an embedded newline is
kept, not truncated; rspamd sorts symbols by absolute weight); fixtures say
seen or composed. The sender check's From: parsing gets no citations: it is
replaced by the port of OpenDKIM's dkim_mail_parse next.

Contradictions left for their own commits: B-G5 cleanAddress, B-PS1 first
key wins, B-PQ1 the forced-expire flag, B-PQ10/PQ11 Postfix's time units.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/milter/testdata/from-lines-other.txt

@@ -5,7 +5,9 @@
 # (internal/milter/sender_test.go) wants each refused; the e2e
 # (test/e2e/dkim_from_test.go) sends each and wants nothing signed for
 # {other}. {OTHER} is {other} in capitals; {other_qp} is {other} with each
-# dot escaped as a quoted pair. One Go-quoted string per line.
+# dot escaped as a quoted pair. One Go-quoted string per line. The lines are
+# composed by hand; that OpenDKIM signs none for {other} is measured, by the
+# e2e on every run.
 "b@{other}"
 "<b@{other}>"
 "\"a@{domain}\"@{other}"

internal/milter/testdata/from-lines-passed.txt

@@ -8,6 +8,8 @@
 # is {domain} in capitals; {other} is another sender of the server, which a
 # line here names in a way the check's scan does not see (a space after the
 # @) - passed by design, and so signed for {domain} alone.
+# The lines are composed by hand; what OpenDKIM signs each with is measured,
+# by the e2e on every run.
 "a@{domain}"
 "<a@{domain}>"
 "\"The Shop\" <Orders@{domain}>"