[wip] ArbSys precompile support

[klkvr]

Motivation

Draft PR implementing support for chain-specific precompiles

Solution

1. Add DatabaseExt::get_block_number method handling NUMBER opcode invocations. Currently it overrides it via l1BlockNumber if we are on arbitrum network.
2. Add ArbSys precompile impl (currently only arbBlockNumber method).
3. Keep track of precompiles for each fork via ForkSpecificPrecompiles which injects and removes precompiles on fork switches.

Impl is not ideal as we'd have to duplicate logic for other chains. This can be made better by only using Ordinary precompiles which do not require DB generic and thus it will be possible to put custom network logic into some kind of object-safe trait which can be then stored on Fork