dev: test account_contract entrypoints

[enitrat]

• Execute from outside is already tested in test_execute_from_outside.cairo

• Some tests are already implemented in test_contract_account.cairo

• Add tests for other entrypoints, using starknet-foudry.

• Modify existing tests, avoiding contract deployment if possible. For example, to test the get_nonce / set_nonce entrypoints, I can use a combination of store / load and internal state of the contract; which is easier than deploying everything.
  Avoid deploying contracts if possible: for simple use cases, you should be able to use a combination of store, load, and internal testing using contract_state_for_testing.

see https://book.cairo-lang.org/ch17-02-testing-smart-contracts.html#accessing-internal-functions-with-contract_state_for_testing