stdlib: Fix m5.ext.pystats __init__.py

Addresses Jason's complaint that wildcare imports should be avoided, in
accordance with PEP008:
https://github.com/gem5/gem5/pull/996#discussion_r1621051601.

Change-Id: I72266df43d3ec4ede3f45c3e34e2e05e1990bd6b

src/python/m5/ext/pystats/__init__.py

@@ -24,11 +24,22 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-from .abstract_stat import *
-from .group import *
-from .jsonloader import *
-from .serializable_stat import *
-from .simstat import *
-from .statistic import *
-from .storagetype import *
-from .timeconversion import *
+from .abstract_stat import AbstractStat
+from .group import (
+    Group,
+    SimObjectGroup,
+    SimObjectVectorGroup,
+)
+from .jsonloader import JsonLoader
+from .serializable_stat import SerializableStat
+from .simstat import SimStat
+from .statistic import (
+    Distribution,
+    Scalar,
+    SparseHist,
+    Statistic,
+    Vector,
+    Vector2d,
+)
+from .storagetype import StorageType
+from .timeconversion import TimeConversion