refactor: use single contracts deployer docker image

[alxdca]

Summary

• Add a single nitro-testnode-contract-deployer:latest image that packages the Nitro contracts and token bridge contracts workspaces.
• Use that deployer image for L2/L3 rollup creation and token bridge creator deployment.
• Remove the separate tokenbridge compose service and deleted docker/tokenbridge.Dockerfile.
• Update token bridge tests and snapshot semantic checks for the new deployment behavior.

Why / Context

• This is useful to remove dependencies on external repo checkouts and separate external Docker images during testnode runtime.
• Packaging the contract deployer flow into one local image makes deployment behavior more reproducible and keeps contract tooling behind one image boundary.
• The L3 rollup path now uses the Docker-based deployment flow instead of the SDK deployment helper, matching the L2 path more closely.