Improved type hints [skip ci]

Author: ankane

pgvector/sparsevec.py

@@ -66,7 +66,7 @@ def to_list(self) -> list[float]:
             vec[i] = v
         return vec
 
-    def to_numpy(self) -> np.ndarray:
+    def to_numpy(self) -> np.ndarray[tuple[int], np.dtype[np.float32]]:
         vec = np.repeat(0.0, self._dim).astype(np.float32)
         for i, v in zip(self._indices, self._values):
             vec[i] = v