valuify blocks.Block

[Jorropo]

blocks.Block being an interface force at least two allocations per blocks ([]byte + the block.Block implementation).
If this was a value struct or even an type Block []byte (we already know the CID in most cases), we would only allocate the []byte and embed or pass by registers (decomposed stack) the rest.

This is gonna break a lot of stuff depending of how brutal we are.

[Jorropo]

List of breakages I find in our orgs:

• https://github.com/ipfs/go-ipld-eth/blob/50e5a9063d1ada296d1bc12d77cc0099a1dc2ad5/eth_block_test.go#L493 archived test.

• go-block-format/blocks.go

  Line 16 in e61d558

  type BasicBlock = blocks.BasicBlock

  stubs, we would obviously remove BasicBlocks from there too.
• https://github.com/filecoin-project/lotus/blob/master/blockstore/mem.go#L70 removes non .BasicBlocks would just dispear if changed since this would not be an interface anymore.
• https://github.com/filecoin-project/venus/blob/e79e1377dffdbac05b0441f1c01a88a154fe03a7/venus-shared/blockstore/mem.go#L69 same code as above.
• https://github.com/filecoin-project/lotus/blob/e51f3e9b159667b6a5cceeb1c7ffab60b7d010d6/api/docgen/docgen.go#L102 docgen, we would replace it by blocks.Block if this is removed.
• https://github.com/filecoin-project/venus/blob/e79e1377dffdbac05b0441f1c01a88a154fe03a7/venus-devtool/api-gen/example.go#L137 same as above