Rework block validator tests to read from actual chainspec

There is a number of cases where values from the prod chainspec are simply hardcoded, even though they may later be compared to actual chainspec values when the tests are run. Additionally, many tests feature hardcoded values for transaction counts that may either be replaced by random numbers, or the chainspec limits. See [https://github.com/casper-network/casper-node/pull/4772](url) for further details.