Fix RSis.CopyWithFreshBuffer

[AlexandreBelling]

Fix CopyWithFreshBuffer

CopyWithFreshBuffer is a method of RSis whose intended role is to enable hashing in parallel by creating short-lived "clones" of the key. The present PR fixes a bug related to this.

Description of the bug

Prior to this PR, CopyWithFreshBuffer would shallow copy the private fields bufM, bufRes and bufMValues. As a result, attempting to use several copies of the same key concurrently results in a race condition (the same buffer being used by all the threads at the same time).

The fix

The proposed fix is to also initialize the rest of the buffers

	res.bufM = make(fr.Vector, len(r.bufM))
	res.bufMValues = bitset.New(r.bufMValues.Len())
	res.bufRes = make(fr.Vector, len(r.bufRes))