Re-enable skipped block list paging unit test

[farazdagi]

What type of PR is this?

Other

What does this PR do? Why is it needed?

• re-enables test that has been marked as skipped on Fix tests depending on configuration flag #5650

Other notes for review

• the issue was rooted in inaccurate state modification in tests, this has been fixed
• params.OverrideBeaconConfigWithReset() has been added and proposed usage inside tests:

resetCfg := params.OverrideBeaconConfigWithReset(params.MainnetConfig())
defer resetCfg()

• this usage makes sure that individual test functions are idempotent
• test setup code has been moved from init() (in one of the tests files) to beacon_test.go:TestMain() (where it is easier to find setup/teardown code for the package).

Note: I will now review all the other code using inaccurate state amendment and file fixing PR (if any) seprately.