Bug: deriving private key will fail if index is larger than that of decryptedShares.length

Maximum index of decrypted shares should be used here instead of `decryptedShares.length` in order to get the correct kCombinations in all instances:

https://github.com/torusresearch/torus.js/blob/0160ae8fb4c622ba44c1e80872da2d17cb0e8650/src/helpers/nodeUtils.ts#L503

This is reproducible in the following scenario:
```
threshold = 3
decryptedShares.count = 3
indexes: [2,3,4]

kCombinations will not include a combination for [2,3,4]
```

Start at src/helpers/nodeUtils.ts around line 503 and inspect how decryptedShares.length determines kCombinations. Reproduce the threshold 3 case with indexes [2,3,4], then verify that the combination [2,3,4] is included when the maximum index exceeds decryptedShares.length.

Written by the indexing model from the issue text.