feat(StdChains): add chain enum, block explorer URLs, and sync with alloy-chains

Hey first time I noticed `StdChains` https://twitter.com/msolomon44/status/1699116841753534877 and checked if we can replace with our internal tooling for this.

Two things that would be quite useful for us is:
- explicit constant getters for the chains defined (aka `StdChains.Arbitrum`)

This is quite handy for when you want to e.g. ensure a script is run on a specific network.

- in `viem` the chain struct also contains the blockexplorer

This is quite handy as you can easily log addresses as blockexplorer link, making them directly clickable.

perhaps could make sense to somehow sync https://github.com/foundry-rs/forge-std/blob/master/src/StdChains.sol#L180 automatically with viem? It's a bit sad that support of chains is so different between:
- StdChains: https://github.com/foundry-rs/forge-std/blob/master/src/StdChains.sol#L180
- viem chains: https://github.com/wagmi-dev/viem/tree/main/src/chains/definitions
- ethers-rs: https://github.com/gakonst/ethers-rs/blob/master/ethers-core/src/types/chain.rs