maintenance: improved docstrings for BCFG

l2geth: better error message for proxying user txs

This commit adds a better error message when there
is an error for proxying user requests to the sequencer.
This allows the change to be relatively backwards compatible
as a good error message is returned when the sequencer url
is not configured.

Enforced import ordering in eslint

go/proxyd: Properly handle null results

Both the `Error` and `Result` fields on `RPCRes` had `omitempty` tags, so null results were being swallowed. We didn't catch this in integration tests because JavaScript tolerates missing keys. This is now fixed by using a custom JSON marshaler.

Fixes #2049

l2geth: Add commands to initialize from a URL, and dump the current chainstate

This PR adds two commands to l2geth:

- `geth init <url> <genesisHash>`, which will download a remote genesis JSON file, compare its hash to the one specified on the CLI, then reinitialize the chain config.
- `geth dump-chain-cfg`, which will dump the current chain config to stdout.

These commands will make it easier for us to adopt the upcoming gas schedule hardfork.

Fixes: ENG-1906

integration-tests: Changes to make it work with live networks again

chore(deps): bump trim-off-newlines from 1.0.1 to 1.0.3

l2geth: fix monotonicity logging bug

feat: add confirmation depth awareness to txmgr

go/proxyd: Cache block-dependent RPCs

test: use hardhat-ethers for importing factories in integration tests

go/proxyd: Add integration tests and batch support

- Fixes ENG-1903

Split OVMMulticall.sol into Multicall.sol & OVMContext.sol in integration tests