Expose forceBuild on fromRegistry()

[donutdaniel]

Summary

• Adds forceBuild option to fromRegistry() in both JS and Go SDKs
• Allows forcing a fresh image pull/rebuild on the base image layer, not just on dockerfileCommands() layers
• JS change is backwards compatible: fromRegistry(tag, secret) still works alongside fromRegistry(tag, { secret, forceBuild })

Test plan

• Verify existing image tests pass
• Test fromRegistry("alpine", { forceBuild: true }) triggers a fresh build
• Test fromRegistry("alpine", secret) still works (backwards compat)

🤖 Generated with Claude Code

[donutdaniel]

motivation was encountering stale images during development, and saw that the python sdk had a force build function (as well as the docker commands nested in the code!). These changes are backwards compatible, but feel free to commandeer or let me know if you'd like to approach it in a different way.

recently I've been pushing a lot of changes and have let my agents loose with docker - and i find that though tagging the more stable and accepted approach, it is also the slower one, so i just use :latest and ran into this problem :p