BotServ BADWORDS: user-configurable regex kicker

BADWORDS <#channel> ADD|DEL|LIST|CLEAR manages a channel's badword
patterns, each a regular expression, so a channel matches whatever it
wants — an improvement over Anope's fixed ANY/SINGLE/START/END. Enable
with KICK <#channel> BADWORDS ON.

Uses the regex crate: it's finite-automata based with linear-time
matching, so untrusted user patterns can't cause catastrophic
backtracking (ReDoS). A channel's patterns compile into one RegexSet
(single-pass match against all of them), cached in the engine and rebuilt
only when the list's revision changes — so the hot path is one is_match
call, no per-message compilation or allocation. Patterns are validated
(and size-limited) at add time; matching is case-insensitive by default.

Cargo.toml

@@ -25,6 +25,7 @@ sha2 = "0.10"
 hmac = "0.12"
 pbkdf2 = { version = "0.12", default-features = false, features = ["hmac"] }
 subtle = "2"
+regex = "1"
 anyhow = "1"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }