fix: set --fault proofs CLI default to true for built in fault-proof networks

All four built-in networks (base-mainnet, base-sepolia, op-mainnet, op-sepolia) have `faultProofs: true` and their `l2oo-address` set to `0x0`. However, the `--fault-proofs` CLI flag defaults to `false`.

A user running a simple command like:

withdrawer --network base-mainnet --withdrawal --rpc --private-key

...gets a crash with: "Fault proofs are required on this network, please provide the --fault-proofs flag".

Since all built-in networks use fault proofs, the default should be `true` to match the network configurations.

**Fix:**
Change the default from `false` to `true` in main.go:
go
flag.BoolVar(&faultProofs, "fault-proofs", true, "Use fault proofs")