plugins: unblock background triggers

[dgw]

The tell, translate, seen, and meetbot plugins all contain match-any rules to run something on any/every message received. Even with #1724 applied, they still cause log spam whenever any ignored user speaks.

Here, I have made the relevant callables in tell, translate, and seen into unblockable functions. There's no reason that ignored users shouldn't receive tell messages, and translate & seen only collect lines passively for use later when commanded by a non-ignored user.

I did not make meetbot's callable unblockable, though. That would allow ignored users to appear in meeting logs despite being blocked from using any commands. Unfortunately this means we'll still get log spam on any instance with meetbot turned on, but when this is combined with #1721 (which makes find's collect-all-lines function unblockable) meetbot will be the only core plugin that causes such a warning with default settings. We can decide to disable it by default, perhaps.

Bonus refactor of translate to use bot.memory instead of a (🤢) global variable.

[Exirel]

global mangle_lines

Ew. Good riddance!