Memory leak in quantile function

Running:
```
#!/usr/bin/env python3
import numpy as np
import datetime
from crick import TDigest

td = TDigest()
for j in range(1000000):
arr = np.array(1)
td.update(arr)
x = td.quantile(0.88)
```

Leads to this memory usage pattern:

Start by reproducing the reported loop with Python, NumPy, and crick's TDigest.quantile call, then inspect the quantile path and its memory behavior. Done means the million-iteration example no longer shows continuing memory growth while preserving the reported quantile behavior.

Written by the indexing model from the issue text.