providers: add BaseLayer

[Lasdw6]

Summary

This PR adds BaseLayer as a self-hosted BrowserArena provider.

BaseLayer is an open-source browser hosting control plane that runs Chromium inside Firecracker microVMs. Unlike managed browser APIs, BaseLayer is benchmarked by provisioning a self-hosted BaseLayer environment and then running the standard BrowserArena hello-browser lifecycle benchmark against it.

What changed

• Added BaseLayerProvider.
• Registered BaseLayer in the provider index and provider type list.
• Added BaseLayer to the us-east runner provider list.
• Added BaseLayer self-provisioning support to scripts/run-and-publish.sh.
• Added BaseLayer logo and leaderboard metadata.
• Labeled BaseLayer as self-hosted on AWS m5zn.metal.

Self-provisioning flow

The BaseLayer provider supports two modes.

If BASELAYER_API_URL is set, BrowserArena uses that existing BaseLayer endpoint directly.

If BASELAYER_API_URL is not set and BASELAYER_AUTO_SELFHOST=1, the runner self-provisions BaseLayer before running the benchmark:

BrowserArena runner
  -> clone BaseLayer from https://github.com/Lasdw6/BaseLayer.git
  -> checkout BASELAYER_REF, default main
  -> run BaseLayer's self-host setup script
  -> provision a single AWS m5zn.metal host
  -> bootstrap Firecracker + Chromium snapshot runtime
  -> run a smoke test
  -> export BASELAYER_API_URL=http://<metal-ip>:3000
  -> run the normal BrowserArena hello-browser benchmark
  -> collect BrowserArena artifacts
  -> terminate the self-hosted metal instance

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[Lasdw6]

Not fully sure how a self-hosted provider should be represented on the leaderboard, so I’d appreciate any input there.