[rules_apple][bundling] `ios_*_test` macho bundle duplicated - 2x disk size / redundant proessing

Given a rules_apple based test bundle - we're facing 2x copies of the macho bundle files. In a repo with 1k tests with hundreds of mb in each test bundle, halving this is a non trivial win.

Note: is orthogonal to https://github.com/bazel-ios/rules_ios/issues/542

Start with the rules_apple-based ios_*_test bundle described in the issue and reproduce the duplicate Mach-O files. Trace the bundling entry point and compare where each copy is produced or consumed. Done means the test bundle contains one copy, disk usage is reduced, and existing Apple test-bundle behavior remains intact.

Written by the indexing model from the issue text.