Encoding FixedBytes uses left-padding instead of right-padding

[2-towns]

The FixedBytes should be encoded by adding trailing zeros (so right padding).

The following test is currently failing:

test "keeps compatibility with FixedBytes":
  let bytes16 = FixedBytes[16](randomBytes[16]())
  check encode(bytes16) == @(bytes16.data) & 16.zeroes

  let bytes32 = FixedBytes[32](randomBytes[32]())
  check encode(bytes32) == @(bytes32.data)

  let bytes33 = FixedBytes[33](randomBytes[33]())
  check encode(bytes33) == @(bytes33.data) & 31.zeroes

The error is:

Check failed: encode(bytes16) == @(bytes16.data) & 16.zeroes
    encode(bytes16) was @[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 22, 123, 248, 85, 22, 17, 155, 159, 163, 175, 32, 209, 119, 44, 3, 33]
    @(bytes16.data) & 16.zeroes was @[22, 123, 248, 85, 22, 17, 155, 159, 163, 175, 32, 209, 119, 44, 3, 33, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

So the current encoding for FixedBytes is using left padding, but it should be using right padding.