Refactor: merge test_ctx and test_ctx2 into one

[KimiWu123]

Describe the feature you would like

To support Beacon chain withdrawals, we added TestContext2 to support 3 generic inputs (number of accounts, number of txs and number of withdrawals). However, it's quite duplicated so we should find a better way to merge them into one. For more details, see discussion here: https://github.com/privacy-scaling-explorations/zkevm-circuits/pull/1634#discussion_r1351330930

Additional context

No response