Cap evidence by absolute number instead of relative size #2590
Description
As of #2560, we cap the amount of evidence allowed in a valid block based on the types.MaxEvidenceBytesPerBlock, which limits it to 1/10 the size of the block.
As discussed in #1637 (comment), we should consider limiting it to an absolute number of pieces of evidence, rather than allocating such a large chunk of the block space.