Support range downloads in the Remote Asset API

This issue is a follow-up to https://github.com/bazelbuild/bazel/issues/22207, which has more context on the motivation and need for range downloads

I'm using https://github.com/chainguard-dev/rules_apko, which depends on range downloads. In bazel >7.1, this is achieved by setting the headers attr.

The remote download APIs currently don't support range downloads, so I can't use `rules_apko` in my bazel workspace.

Start by reading the linked issue 22207 for the motivation and requirements, then inspect the current Remote Asset API download definitions. The work is complete when the remote download API supports range downloads needed by rules_apko; the issue names no files or tests, so further code and validation points must be located.

Written by the indexing model from the issue text.