irc, config: config options for flood penalty on longer messages

[Exirel]

Description

It was asked by someone on IRC so I added some config options to control extra wait penalty on longer messages, and one thing led to another I also added a setting to control the maximum wait time because why not.

I've to say that @dgw was right again, but maybe even more "on the nose" than ever before:

07:22:51 <+dgw> It's some arcane magic from AT LEAST a decade ago.
         https://github.com/sopel-irc/sopel/blame/d610029b3933c2ddd6751a7523dd12a30cf4ae8b/irc.py#L139
07:23:24 <+dgw> actually 11
         https://github.com/sopel-irc/sopel/blame/c79635a1627813028d48b2cd0a5e226cd116bae5/irc.py#L135
07:23:28 <+dgw> "Initial commit"
07:23:33 <+dgw> can't get older than that
[...]
07:25:19 <+dgw> also, like half the code in Sopel makes me go hmm

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make quality and make test)
• I have tested the functionality of the things this change touches

[dgw]

Here we have a first pass. I probably missed some things, but caught most issues that actually matter. 😹

[Exirel]

@dgw I applied your changes and improved the debug log. Ready for re-review at your convenience.

[dgw]

Let's 🚢 it

[Exirel]

🐑 🐑 🐑 🐑