fix: add HOST_IP support to reth entrypoint

[mehmetkr-31]

Summary

Adds HOST_IP support to the reth execution client entrypoint, completing parity with geth and nethermind.

Problem

The geth-entrypoint has long supported HOST_IP via --nat=extip, and nethermind-entrypoint now supports it via --Network.ExternalIp. The reth-entrypoint is the only execution client that ignores HOST_IP, causing reth operators running behind NAT to have degraded peer discovery and lower peer counts.

Solution

Add the same conditional check (if [ "${HOST_IP:+x}" = x ]) to the reth entrypoint and append --nat=extip:$HOST_IP to ADDITIONAL_ARGS.

Verification

The --nat=extip:<IP> flag is a valid reth CLI argument. Verified against the upstream reth source code:

• crates/node/core/src/args/network.rs defines the --nat argument as a NatResolver with supported values: any|none|upnp|publicip|extip:<IP>.
• crates/net/nat/src/lib.rs implements NatResolver::ExternalIp(IpAddr), which is the enum variant triggered by --nat=extip:<IP>.

References:

• https://github.com/paradigmxyz/reth/blob/main/crates/node/core/src/args/network.rs
• https://github.com/paradigmxyz/reth/blob/main/crates/net/nat/src/lib.rs

Impact

• Reth operators can now advertise their public IP for better P2P peer discovery.
• All three supported execution clients (geth, nethermind, reth) behave consistently when HOST_IP is configured.

Checklist

• Change is minimal and focused.
• Follows the same pattern used in geth-entrypoint.
• Flag verified against upstream reth source code.
• No breaking changes.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1