fix: reject autocommit=False override and IS NULL condition handling

_where() rendered None conditions as col = %s bound to NULL, which sql
never matches, so get/get_one/exists/delete silently missed NULL rows
despite insert() writing NULL fine — fixed to emit col IS NULL, in
lockstep with the psql lib's identical fix.

Separately, __init__ now rejects autocommit=False in pool_kwargs: with
it, _run/_fetchall never commit, so on pool release aiomysql closes the
in-transaction connection and MySQL rolls back server-side while
insert()/delete()/upsert()/execute() still return success signals
(lastrowid/rowcount) for writes that were silently discarded.

Signed-off-by: disqualifier <dev@disqualifier.me>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "mysql"
-version = "0.1.2"
+version = "0.1.3"
 description = "async mysql/mariadb wrapper over aiomysql: two-layer API (friendly verbs + raw escape hatch), fail-loud, config-free"
 requires-python = ">=3.10"
 dependencies = [