* ethclient/gethclient: improve time-sensitive flaky test

* eth/catalyst: fix (?) flaky test

* core: stop blockchains in tests after use

* core: fix dangling blockchain instances

* core: rm whitespace

* eth/gasprice, eth/tracers, consensus/clique: stop dangling blockchains in tests

* all: address review concerns

* core: goimports

* eth/catalyst: fix another time-sensitive test

* consensus/clique: add snapshot test run function

* core: rename stop() to stopWithoutSaving()
Co-authored-by: Felix Lange <fjl@twurst.com>