fix: ensure that accumulated orphan chain data is committed before header validation

[sdbondi]

Description

• commit orphan chain accumulated data before orphan header validation so that
  accumulated target difficulty is available for chain comparison
• use hash for reorg chain rewind because the height value of the candidate block is not yet
  checked against the fork height.
• improve test infra to allow blockchain tests to be easily be constructed
• add a failing test for the fix in the PR

Motivation and Context

Observed errors:

2021-10-10 09:17:19.987800805 [c::cs::database] WARN  Discarding orphan 0291ba64d777e46016ca7b055bdf6979c1fe11bf31b78a7c20d507cb69c3f293 because it has an invalid header: FatalStorageError("The requested chain_header_in_all_chains was not found via hash:9c2c5734a783d891b617905e27e861ac1595760d5c22335c8d31feb7dc38a2a5 in the database")

The above error occurs because of orphan accumulated data was set in the DbTransaction but is not
actually committed to lmdb. This manifests as a validation error and was not picked up by other tests because
the validator was mocked out.

The solution in this PR is to write the transactions as needed. This means that in a rollback situation, the
accumulated orphan chain data will remain. That should be ok since that data can be overwritten/replaced
on the next reorg evaluation if needed.

This demonstrates the shortcomings of the current approach and the need for the calling code in
BlockchainDatabase<B> to have access to ACID DB transactions.
I have played with the idea of abstracting and generifying atomic transactions but found the need for GAT to get it to work. We no longer
have or use any other BlockchainBackend impl other than LMDB so leaking LMDB Read,WriteTransaction
may be acceptable. Passing the transaction in to every function in BlockchainBackend may be a deal breaker.

How Has This Been Tested?

• Issue reproduced in handle_possible_reorg::it_links_many_orphan_branches_to_main_chain
• Manually (not necessarily tested, the base node runs for a day and is still at the tip)

Consolidated some of the existing "blockchain builder" test infra that was duplicated and added
a declarative macro for building chains let specs = block_spec!(["A->GB"], ["B->A", difficulty: 100]);

[stringhandler]

Nice. It's a little more complicated with all the new individual transactions, but as you said, this should eventually be changed to allow a better transaction model.