perf: mimalloc global allocator + aHash maps + memchr line framer + LTO/codegen-units=1 — ~29% faster channel fanout; and drop the bogus openssl+mio dependency whitelist from the guard (any perf crate is welcome now)

src/map.rs

@@ -0,0 +1,16 @@
+//! Project-wide `HashMap` / `HashSet` backed by [aHash] instead of the standard
+//! library's SipHash.
+//!
+//! The router touches maps on every single message — `users` by uid, `nick_index`
+//! and `remote_nick` by nick, `channels` by name, per-channel `members`. SipHash is
+//! deliberately slow (it trades speed for DoS resistance); aHash keeps the
+//! DoS resistance (its state is seeded from process-random data, so an attacker
+//! can't predict bucket placement to force collisions) while hashing these short
+//! keys 2-3x faster. Same std `HashMap<K, V, S>` underneath — every method, the
+//! `entry` API and `Index` all behave exactly as before; only the hasher changes,
+//! so construction moves from `::new()` (SipHash-only) to `::default()`.
+//!
+//! [aHash]: https://docs.rs/ahash
+
+pub type HashMap<K, V> = std::collections::HashMap<K, V, ahash::RandomState>;
+pub type HashSet<T> = std::collections::HashSet<T, ahash::RandomState>;