Batch Merkle Proof - override equals for matcher array equality

[ApexTheory]

Required for ergoplatform/ergo#1526

ScalaTest matchers do not properly evaluate Array contents as per scalatest/scalatest#491.
Even when defining a custom Equality[BatchMerkleProof] trait, it does not get invoked when the target object is wrapped inside another container. This was causing problems in the Ergo Node PoPow serialization tests,

As we are not using BatchMerkleProof inside any hash-based collections, I think we can avoid overriding hashcode as well?

Open to any alternative suggestions.

[kushti]

Based on zip definition:

def zip[A1 >: A, B, That](that: GenIterable[B])(implicit bf: CanBuildFrom[Repr, (A1, B), That]): That = {
    val b = bf(repr)
    val these = this.iterator
    val those = that.iterator
    while (these.hasNext && those.hasNext)
      b += ((these.next(), those.next()))
    b.result()
}

that can be equal to this if indices and proofs are prefixes just, so not strict equality is really checked.

Please rewrite equals with comparing length of collections first, then doing by-index loops with per-element comparison (using .apply() from Seq), so avoiding collections re-allocations also