add explicit IRC-aware comparison keys

docs/plugin-api-additions/names.md

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+# Explicit IRC comparison keys
+
+`IRCName(text, context=None, casemapping=None, connection_id=None)` is an
+immutable helper, not a str subclass. Construct it explicitly for dictionary/set
+keys; existing get_info/list/event values remain normal strings.
+Equality and hashing include the connection ID and captured casemapping, so
+identical-looking names on different connections are different keys. An IRCName
+never compares equal to a plain str. `str(key)` / `key.text` recover the spelling.
+
+`irc_casefold(text, casemapping='rfc1459')` supports ascii, strict-rfc1459 and
+rfc1459. Only ASCII IRC characters fold; Unicode casefold would be incorrect.
+The new `get_info('casemapping')` reports the comparator actually used by core.
+Current master handles ASCII and RFC1459; this patch does not change its handling
+of advertised strict-rfc1459. An explicit mapping is available for scripts that
+need strict-rfc1459 independently. Keys capture their mapping so hashes stay
+stable; rebuild a collection if the connection's mapping changes.
+
+```python
+seen = {zoitechat.IRCName('[SomeNick]')}
+assert zoitechat.IRCName('{somenick}') in seen  # RFC1459 connection
+```