Typed shell for RemoteCacheItSteps.prePull (drop raw generate warnings)

[russwyte]

Problem

Dogfood Aggregate test uses RemoteCacheItSteps.prePull as extraSteps. That bundle is built with Script.raw / Steps.built, so every zipxWorkflowGenerate dumps many warnings:

zipx: step bundle 'pre-pull-remote-cache-images' uses a raw escape hatch, which nothing validates: …

The Aggregate verify sbt session is already typed (zipxTasks.session(test, plugin / scripted)). The remaining noise is this pre-pull shell.

Goal

Rewrite project/RemoteCacheItSteps.scala with typed zipx.shell (Script / Exec / loops or equivalent) so prePull.rawFragments is empty and generate is quiet for dogfood.

Keep behavior: retrying docker pull for RemoteCacheProof.image and RemoteCacheProof.sbtFixtureImage (saferis-style Hub latency outside the test JVM; Ryuk stays on).

Notes

• Source: project/RemoteCacheItSteps.scala
• Wired from root build.sbt Aggregate Capability.once(…, extraSteps = RemoteCacheItSteps.prePull)
• Related: typed SbtCommand work in Typed SbtCommand: keys in the plugin, wire form in core #93 (sbt side cleaned; this is the shell side)