Move env:pull auto-retry logic to docker.js

[desrosj]

This moves the retry mechanism added in r62857 from the GitHub Actions workflow to the env:pull command, which is a benefit any time the command is run, not just in the PHPUnit workflow.

Trac ticket: Core-65722

Use of AI Tools

Claude Code created the initial draft of this PR.

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[irozum]

This cleanly generalizes the retry-on-pull logic from the CI-only bash loop (r62857) into docker.js itself, so it benefits env:pull wherever it's invoked, not just the reusable PHPUnit workflow. It also correctly leaves every other docker.js subcommand (down, run, exec, etc.) untouched, since maxAttempts is only >1 when the first arg is pull.

Since a real registry timeout isn't reliably reproducible, I stubbed a fake docker binary on PATH to exercise the loop directly: a fail-fail-succeed sequence retries at 10s then 20s and exits 0 on the third attempt, an always-failing pull exhausts exactly 3 attempts and exits non-zero, and a non-pull command (down) fails immediately with no retry/sleep at all. All three matched the ticket's spec exactly. The synchronous Atomics.wait sleep is a reasonable choice here given this is a blocking CLI wrapper with no concurrent I/O to preserve.

No blocking concerns. I couldn't run the JS lint step — wp-scripts lint-js is currently broken in my checkout on an unrelated zod dependency resolution error that reproduces on trunk too — but the diff's style (tabs, single quotes, template literals) matches the rest of the file.