feat: add multi-server support

Connect to multiple IRC servers concurrently from a single config file.
Plugins are loaded once and shared; per-server state is isolated via
separate SQLite databases and per-bot runtime state (bot._pstate).

- Add build_server_configs() for [servers.*] config layout
- Bot.__init__ gains name parameter, _pstate dict for plugin isolation
- cli.py runs multiple bots via asyncio.gather
- 9 stateful plugins migrated from module-level dicts to _ps(bot) pattern
- Backward compatible: legacy [server] config works unchanged

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_urltitle.py

@@ -25,7 +25,7 @@ from plugins.urltitle import (  # noqa: E402, I001
     _extract_urls,
     _fetch_title,
     _is_ignored_url,
-    _seen,
+    _ps,
     on_privmsg,
 )
 
@@ -40,6 +40,7 @@ class _FakeBot:
         self.sent: list[tuple[str, str]] = []
         self.nick = "derp"
         self.prefix = "!"
+        self._pstate: dict = {}
         self.config = {
             "flaskpaste": {"url": "https://paste.mymx.me"},
             "urltitle": {},
@@ -334,26 +335,28 @@ class TestFetchTitle:
 
 class TestCooldown:
     def setup_method(self):
-        _seen.clear()
+        self.bot = _FakeBot()
 
     def test_first_access_not_cooled(self):
-        assert _check_cooldown("https://a.com", 300) is False
+        assert _check_cooldown(self.bot, "https://a.com", 300) is False
 
     def test_second_access_within_window(self):
-        _check_cooldown("https://b.com", 300)
-        assert _check_cooldown("https://b.com", 300) is True
+        _check_cooldown(self.bot, "https://b.com", 300)
+        assert _check_cooldown(self.bot, "https://b.com", 300) is True
 
     def test_after_cooldown_expires(self):
-        _seen["https://c.com"] = time.monotonic() - 400
-        assert _check_cooldown("https://c.com", 300) is False
+        seen = _ps(self.bot)["seen"]
+        seen["https://c.com"] = time.monotonic() - 400
+        assert _check_cooldown(self.bot, "https://c.com", 300) is False
 
     def test_pruning(self):
         """Cache is pruned when it exceeds max size."""
+        seen = _ps(self.bot)["seen"]
         old = time.monotonic() - 600
         for i in range(600):
-            _seen[f"https://stale-{i}.com"] = old
-        _check_cooldown("https://new.com", 300)
-        assert len(_seen) < 600
+            seen[f"https://stale-{i}.com"] = old
+        _check_cooldown(self.bot, "https://new.com", 300)
+        assert len(seen) < 600
 
 
 # ---------------------------------------------------------------------------
@@ -361,8 +364,6 @@ class TestCooldown:
 # ---------------------------------------------------------------------------
 
 class TestOnPrivmsg:
-    def setup_method(self):
-        _seen.clear()
 
     def test_channel_url_previewed(self):
         bot = _FakeBot()