selftest: cover the assembly half of the block limits

consensus-limits only ever asked what CheckBlock() refuses. Nothing asked what
the assemblers produce, which is why a miner able to overshoot the cap by an
entire mempool sat here unnoticed through both the deployed and candidate
builds.

Adds the other half: a template built from a 3 MB mempool stays inside the
budget and passes CheckSizeLimits(); a transaction too big for the budget is
skipped while the ones that fit are still taken; sigop-heavy transactions stop
selection at MAX_BLOCK_SIGOPS while the block is still small. Plus the rule's
edges, including that sigops exactly on the limit fit -- CheckBlock() fails on
`>`, so assembly must accept what validation accepts.

The test drives BlockTemplateFits the way the assemblers drive it rather than
calling them: BitcoinMiner needs a CTxDB, a wallet key and cs_main, and
RebuildJob is static in rpc.cpp. What that proves is the shared rule and the
property it exists to give, which is where the defect was -- the budget was
right and the enforcement was not.

Checked against the bug: with the fit test neutered, eight of these fail,
including both templates that CheckBlock() would have rejected. With the sigop
comparison stricter than CheckBlock's by one, the boundary case fails.

0 files changed, 0 insertions, 0 deletions