Update Anvil instances to use `.on_anvil*` on the ProviderBuilder for most cases

[zerosnacks]

• Including examples that require keys() by using provider.get_accounts() + .on_anvil_with_wallet*
• Excluding examples that exist to show specific behavior around wallets or things that .on_anvil abstracts away
• Unify the way we pass in URLs, prefer a variable rpc_url
• Prefer anvil.endpoint_url() instead of anvil.endpoint().parse()?