I've noticed that test(s) in github.com/ssvlabs/ssv/utils/hashmap package consume up to 8GB of memory when running, sometimes it even results in the test being killed by OS:

ok  	github.com/ssvlabs/ssv/utils/format	1.012s	coverage: 70.8% of statements
PASS
coverage: 100.0% of statements
signal: killed
FAIL	github.com/ssvlabs/ssv/utils/hashmap	9.973s
ok  	github.com/ssvlabs/ssv/utils/rsaencryption	1.895s	coverage: 56.8% of statements

There seems to be a memory leak (creating Timer objects in almost infinite loop that is forcefully broken by Test terminating its run). This PR fixes it, and cleans up a bit.

I've also checked all other places in this repo that could have had similar issues (when combining for{}, select, time.After) and found only 1 other test affected by this: #1781