Use the least latent builder

[rob-maron]

A previous PR allowed us to specify multiple builders via the command line #3693

This PR changes the builder client flow so that, when configured with a list, it will always try to use the least latent one. This will allow us to deploys builders in multiple regions and significantly decrease latency there

The flow is now as follows:

1. Block info will be requested from each builder simultaneously (this is block metadata - not the full block). The first builder to respond is treated as the fastest, the second is the second fastest, and so on
2. Starting with the fastest builder, we sort the block infos it responded with by largest to smallest (block) and begin trying to claim them
3. If all claims fail, we go back to step 2 with the next fastest builder

The simpler solution would be to simultaneously try to claim blocks from every builder at once. The main disadvantage is that it may have us propose with a smaller block from a builder that is further away, rather than a larger block from a builder that is closer. And it would potentially increase resource usage on the builders as well