chore(types): Tighten validation on `Block` modifiers

Right now we have the ability to set things like `base_fee_per_gas` on a `Block` class in a `blockchain_test`. This can lead to silent errors when filling because this isn't validated against the value that comes back from EELS via t8n. See the example [here](https://github.com/ethereum/execution-spec-tests/pull/2262).

We should likely require that a test that sets fields like these be marked with `pytest.mark.exception_test`.

We should make sure that we have fail-safes for `header_verify`, `rlp_modifier`, and fields that change the fixture objects post-t8n validation like the case described in the linked PR here.

Opening this issue to discuss the best approach for this.