* Add stats and counter around cost model ops, mainly:
- calculate transaction cost
- check transaction can fit in a block
- update block cost tracker after transactions are added to block
- replay_stage to update/insert execution cost to table
* Change mutex on cost_tracker to RwLock
* removed cloning cost_tracker for local use, as the metrics show clone is very expensive.
* acquire and hold locks for block of TXs, instead of acquire and release per transaction;
* remove redundant would_fit check from cost_tracker update execution path
* refactor cost checking with less frequent lock acquiring
* avoid many Transaction_cost heap allocation when calculate cost, which
is in the hot path - executed per transaction.
* create hashmap with new_capacity to reduce runtime heap realloc.
* code review changes: categorize stats, replace explicit drop calls, concisely initiate to default
* address potential deadlock by acquiring locks one at time
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