Improve speed of ./tests package speed

[AskAlexSharov]

github.com/erigontech/erigon/tests 407.674s

last bottleneck i know:

• rwtx got committed (while can be rolledback)
• it creating many databases on disk - and seems disk is the bottleneck (maybe ramfs can be used)
• it seems ./tests - tests are mostly for stage_exec, but it using all components: Caplin, etc... maybe we should make them a bit lower-level (more like 'unit-tests' rather than 'integration')

[dvovk]

I spent some time investigating what is going. The main time consuming parts is read write to disk. I don't see anything specific what can be done to it but in fact it is pretty fast as I got average speed per test around 60ms and it just the amount of tests which is thousands. I tried to use ramps but it didn't make any positive results. What I've done is make tests to run in parallel which increased performance by 25% #12527

[dvovk]

For integration tests I did more investigation and related to it make sense to have parallel execution only for BlockTest as other test doesn't shows any significant improvement or even get worse in performance:

File	Test func	Test name	Tests count	Total time seconds (parallel)	Average time per test ms (parallel)
block_test.go	TestBlockchain	BlockTest	616	41 (26)	66.8 (42.2)
difficulty_test.go	TestDifficulty	- (func)	18598	2.65 (5.96)	0.14 (0.32)
exec_spec_test.go	TestExecutionSpec	BlockTest	5049	324 (211)	64.2 (41.7)
rlp_test.go	TestRLP	RLPTest	81	2.45 (2.48)	30.2 (30.6)
state_test.go	TestState	StateTest	16457	206.6 (205.5)	12.5 (12.4)
transaction_test.go	TestTransaction	TransactionTest	237	3.2 (5.74)	13.5 (24.2)