* implement draft/pre-away
* clean up some subtleties in auto-away aggregation.
* consistently apply auto-away only to always-on
* `AWAY *` should not produce user-visible changes wherever possible

Sanitize the in-band error message from REHASH

TAGMSG should not get automatic RPL_AWAY replies

Add WHO responses for services

According to the de facto standard, `AWAY :\r\n` is equivalent to `AWAY\r\n`.
Our behavior was inconsistent before, now it consistently matches the de facto
standard.

WHO <nickname> should not respect +i

Sanitize ::1 to 0::1 in WHOX output

* Add ACCEPT-tracking functionality (authorizing users to send DMs
  despite +R or other applicable restrictions)
* Sending a DM automatically accepts the recipient
* Add explicit ACCEPT command

Add more clarify in NS INFO and SAREGISTER about unregistered nicknames

Fixes #1924

`NICK :` pre-registration needs to be special-cased to immediately
send ERR_NONICKNAMEGIVEN (unlike erroneous nonempty nicknames,
which are processed when registration is complete)

LIST should not return ERR_NOSUCHCHANNEL for nonexistent channels

* Fix #1911 +s channels don't appear in /list even though on the channel

* use channel.HasClient instead of custom iterative checker

Include server start time in INFO output.

Having the 'samode' capability made all KICK commands privileged. This appears
to have been introduced unintentionally by 42316bc04f and I can't find
any discussion of a rationale. Since this goes against our policy that all
ircop (as opposed to channel founder) privileges must be invoked explicitly
(e.g. SAJOIN, SAMODE), remove this.

This extends #1650 to cover WHO as well as WHOIS

The arithmetic was assuming that the nickname is * (which it is
pre-registration). However, we were sending the actual nickname
post-registration. It would be simpler to always send *, but it
appears that the nickname is actually required by the spec:

>Replies from the server must [sic] contain the client identifier name or
>asterisk if one is not yet available.

Jobe points out that 0 is a valid oplevel in some contexts,
* is a better placeholder for "unimplemented".

See discussion on #1852

From discussion with @emersion, this will help with UX if people try to
log into their unverified accounts.

Account registrations pending verification should produce a logline and
send a sno.

Reported by @mogad0n; the mute mask was being case-canonicalized,
but the RELAYMSG identifier wasn't being case-canonicalized before
the check.

`WHO #channel o` is supposed to return only server operators.
This is RFC1459 cruft; just return an empty list in this case.

RPL_ENDOFWHO should send the original, un-normalized mask

Ensure the pagination window is full by making sure that every history item
gets a replay line in CHATHISTORY output, even TAGMSG.

This reverts commit 5bbee02fe6.

Fix various pagination issues with CHATHISTORY; also undo #491
(msgid munging).

Fixes #1787

Warn if the user sent, e.g., /QUOTE /SAMODE instead of /QUOTE SAMODE

Refs:

* other instances in the codebase
* https://defs.ircdocs.horse/defs/numerics.html#err-needmoreparams-461
* https://modern.ircdocs.horse/#errneedmoreparams-461

For consistency with RFC2812, Bahamut, Hybrid, Insp, Plexus4, Unreal.
https://datatracker.ietf.org/doc/html/rfc2812#section-3.2.8

At the expense of consistency with chary/solanum, irc2, and ircu2.

reported by @Mikaela

We can check once during initialization of the SASL session, e.g.
on receiving `AUTHENTICATE PLAIN` or `AUTHENTICATE EXTERNAL`

See: https://github.com/ircv3/ircv3-specifications/pull/466