blade_embedding raises runtime divide by zero warning

[sgrava]

Investigate and fix RuntimeWarning: divide by zero... in blade_embedding.

Description

Running the blade algorithm, it is common to get a warning:

qoolqit/embedding/algorithms/blade_embedding/_helpers.py:9: RuntimeWarning: divide by zero encountered in divide
  return 1 / dist**6
qoolqit/embedding/algorithms/blade_embedding/_helpers.py:13: RuntimeWarning: divide by zero encountered in divide
  return (1 / weight) ** (1 / 6)  # type: ignore[no-any-return]

To reproduce

import numpy as np
from qoolqit import BladeEmbedder
qubo = np.array([[0,1],[1,0]], dtype=np.float64)
embedder = BladeEmbedder()
graph = embedder.embed(qubo)