Fix Shelby private beta chain ID on v3.5

[zjma]

Summary

• backport the Shelby private beta chain ID fix to release-v3.5
• route Aptos chain_id 125 to the configured shelby-private-beta RPC instead of stale chain_id 139
• add a small regression test that keeps 125 wired and rejects the old 139 route

Validation

• cargo check -p network-node
• cargo test -p network-node
• git diff --check

Release note

NEXT_RELEASE on release-v3.5 is already 3.5.1, so after this merges the release commit should tag v3.5.1 and bump NEXT_RELEASE to 3.5.2.