Replace dry run mode with a test relay

[dvush]

📝 Summary

• removes dry run mode and validation from the rbuilder
• adds a test_relay binary that is used to accept and validate submissions
• removes optimistic mode validation feature

💡 Motivation and Context

Dry run mode does not allow us to fully test submissions to the relays so here its replaced with separate service that implements relay API.

Test builders does not need to point to real relays as test relays can server validator data itself. This improves robustness in the tests as production relays are not even mentioned in the test builder configs.

✅ I have completed the following steps:

• Run make lint
• Run make test
• Added tests (if applicable)

[github-actions]

Benchmark results for 1a2d1ed

Report: https://flashbots-rbuilder-ci-stats.s3.us-east-2.amazonaws.com/benchmark/1a2d1ed-41e41c2/report/index.html

Date (UTC)	2025-02-11T16:06:20+00:00
Commit	1a2d1edad03b56aa5d6a73132de634e5eccb50d9
Base SHA	41e41c27fe3cc3019ea5e7e0cac46c109fdb4591

Significant changes

Benchmark	Mean	Status
gather_nodes_storage_tries	-8.45%	Performance has improved.
cloning_3000_branch_node_size_elements	2.19%	Performance has degraded.
MEV-Boost SubmitBlock serialization/JSON encoding	3.83%	Performance has degraded.

[metachris]

Would it make sense to add a short section to the README about the fake relay? I.e. what it does, how to start and how to use it, maybe what's the plans with it if there's further work planned?