fix(anvil): return correct block number for Arbitrum fork

[grandizzy]

Motivation

Closes #6749

Solution

• use storage.best_number for eth_blockNumber call
• make sure best number is not overwritten when new blocks are mined
• dump and load best_number from state file
• fix issue reported with Arbitrum chain specifics not applied if --chain-id missing eth_blockNumber returns L1 block for Arbitrum fork #6749 (comment) by calling apply_chain_and_block_specific_env_changes after chain id fetched from provider

[mattsse]

cool, ty!