fix: Trim the ending slash from consensus RPC

[kvinwang]

Without this fix, helios doesn't work when --consensus-rpc is given:

$ cargo run -- ethereum --rpc-port 14433 --network mainnet --execution-rpc https://ethereum-rpc.publicnode.com --consensus-rpc https://ethereum.operationsolarstorm.org
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.40s
     Running `target/debug/helios ethereum --rpc-port 14433 --network mainnet --execution-rpc 'https://ethereum-rpc.publicnode.com' --consensus-rpc 'https://ethereum.operationsolarstorm.org'`
2025-01-08T02:21:17.908637Z  INFO helios::rpc: rpc server started at 127.0.0.1:14433
2025-01-08T02:21:18.591966Z ERROR helios::consensus: sync failed err=could not fetch bootstrap: rpc error on method: bootstrap, message: status: 404, raw response: b""

[ncitron]

LGTM!