Fix ErgoStateContextSpec Sporadic Failures

[stenolog]

closes #2114

[kushti]

Good catch!

For

var imvValue = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize + 1).sample.get
    while (imvValue._1.head == 0) {
        imvValue = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize + 1).sample.get
    }
    sc.appendFullBlock(fbWithFields(imvValue +: oldFields)) shouldBe 'failure

the issue is that extensionKvGen is defined as

  def extensionKvGen(keySize: Int, valuesSize: Int): Gen[(Array[Byte], Array[Byte])] = for {
    key <- genSecureBoundedBytes(keySize, keySize)
    value <- if (key.head == 0) genSecureBoundedBytes(4, 4) else genSecureBoundedBytes(valuesSize, valuesSize)
  } yield (key, value)

so when imvValue._1.head == 0, value is 4 bytes long, not 65 (Extension.FieldValueMaxSize + 1)

I think dedicated generator should be used for the check

[kushti]

for

var validMKV = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize).sample.get
while (validMKV._1.head != 1) {
  validMKV = extensionKvGen(Extension.FieldKeySize, Extension.FieldValueMaxSize).sample.get
}

generation of test data here is good, as for validMKV._1.head == 1 interlinks would be packed improperly, and interlinks packing/unpacking is tested in another test

[stenolog]

while (validMKV._1.head != 1) {

It's validMKV._1.head == 1

This fails, too, there are two different sporadic failures.

[kushti]

@stenolog remove

printf("\r%d05 ", i)

and for loop added, not related to fixes

[kushti]

I think custom generators should be used , reiterating over extensionKvGen is messy . As your goal is to avoid specific key spaces anyway, better to do that directly