feat: define Metric.Snowflaking (#33114)

From https://github.com/urkud/SardMoreira

This is a copy of the original space with distance redefined to be `d x y = (dist x y) ^ α`.

Author: urkud

Mathlib.lean

@@ -7240,6 +7240,7 @@ public import Mathlib.Topology.MetricSpace.Pseudo.Real
 public import Mathlib.Topology.MetricSpace.Sequences
 public import Mathlib.Topology.MetricSpace.ShrinkingLemma
 public import Mathlib.Topology.MetricSpace.Similarity
+public import Mathlib.Topology.MetricSpace.Snowflaking
 public import Mathlib.Topology.MetricSpace.ThickenedIndicator
 public import Mathlib.Topology.MetricSpace.Thickening
 public import Mathlib.Topology.MetricSpace.TransferInstance