feat(forge): sanity checks before executing a script

### Component

Forge

### Describe the feature you would like

Do sanity checks before starting to send transactions for a `forge script`.

### Additional context

- So many times i have entered the wrong Etherscan API key for whatever reason and had to either redeploy (if possible) or verify manually (sanity check would make sure my API key is valid)
- Same for gas estimation, i would set the `--gas-estimate-multiplier` to `200` or something -- script would start sending transactions and die in the middle (sanity check would make sure my account has enough ETH)

Im sure people would have other (better) ideas for more sanity checks. Either way that sort of feature would be a big UX improvement and could potentially save a lot of pain and resources for users.

The issue names the forge script command but no files or tests. Start by tracing the command's transaction-sending path and identify where API-key validation and gas-funding checks could be defined. Done should include an agreed, tested set of pre-execution sanity checks that prevents avoidable mid-script failures.

Written by the indexing model from the issue text.