* core: use uint64 for total tx costs instead of big.Int

* core: added local tx pool test case

* core, crypto: various allocation savings regarding tx handling

* Update core/tx_list.go

* core: added tx.GasPriceIntCmp for comparison without allocation

adds a method to remove unneeded allocation in comparison to tx.gasPrice

* core: handle pools full of locals better

* core/tests: benchmark for tx_list

* core/txlist, txpool: save a reheap operation, avoid some bigint allocs
Co-authored-by: Martin Holst Swende <martin@swende.se>