feat: add human-readable datetime formatting and !lastshow command

IRC plugins now format datetimes as "Wed Mar 11, 10:00 PM EDT" instead
of raw ISO 8601. Configurable timezone defaults to America/New_York.

Adds !lastshow N command to both Limnoria and Sopel plugins, returning
track N from the previous week's show via existing API endpoints.

Made-with: Cursor

tests/test_format_dt.py

@@ -0,0 +1,57 @@
+"""Tests for the format_dt helper used by both IRC plugins.
+
+The function is duplicated in both plugins (Limnoria and Sopel) since they
+can't share imports. This tests the logic independently of either IRC framework.
+"""
+from datetime import datetime
+from zoneinfo import ZoneInfo
+
+
+def format_dt(iso_string: str | None, tz_name: str = "America/New_York") -> str:
+    if not iso_string:
+        return "never"
+    dt = datetime.fromisoformat(iso_string)
+    local = dt.astimezone(ZoneInfo(tz_name))
+    return local.strftime("%a %b %-d, %-I:%M %p %Z")
+
+
+def test_format_dt_est():
+    result = format_dt("2026-01-15T03:00:00+00:00")
+    assert result == "Wed Jan 14, 10:00 PM EST"
+
+
+def test_format_dt_edt():
+    result = format_dt("2026-03-12T02:00:00+00:00")
+    assert result == "Wed Mar 11, 10:00 PM EDT"
+
+
+def test_format_dt_none():
+    assert format_dt(None) == "never"
+
+
+def test_format_dt_empty_string():
+    assert format_dt("") == "never"
+
+
+def test_format_dt_custom_timezone():
+    result = format_dt("2026-03-12T02:00:00+00:00", "America/Chicago")
+    assert "CDT" in result or "CST" in result
+
+
+def test_format_dt_no_seconds_or_microseconds():
+    result = format_dt("2026-03-12T02:30:45.123456+00:00")
+    assert ":45" not in result
+    assert ".123456" not in result
+    assert "10:30 PM" in result
+
+
+def test_format_dt_single_digit_day():
+    result = format_dt("2026-03-05T03:00:00+00:00")
+    assert "Wed Mar 4," in result
+    assert " 04," not in result
+
+
+def test_format_dt_single_digit_hour():
+    result = format_dt("2026-01-15T06:00:00+00:00")
+    assert "1:00 AM" in result
+    assert "01:00" not in result