* rework bucket txs
* introduce max_block_weight to global (based on chain_type)
not yet in use anywhere...
* now using global::max_block_weight() everywhere
* testing max_block_weight needs to be big enough to cover existing chain tests...
* add some test coverage for prepare mineable transactions at the block weight limit
introduce AsLimitedTx{max_weight} so we can build artifically small blocks (per mining config)
* cleanup
* default_mineable_max_weight is just the default max_block_weight
we do not need to account for coinbase reward here (tx vs block)
* 75 change outputs in a test is not valid now that we have a low block weight limit...
