Instead of writing file content to /tmp (which broke relative imports
like codecs/asn1.zig), symlink the original file's directory into
.zig-cache/tmp/zig0_test. This keeps the module root outside lib/std/
(avoiding module path conflicts) while preserving subdirectory import
resolution through the symlink.
In verbose_air.zig, use Compilation.Path.fromUnresolved to construct the
module root so it gets the same canonical root enum (.local_cache, etc.)
as file paths computed during import resolution, avoiding isNested
root mismatches.
Fixes the codecs.zig test failure (434/434 tests now pass).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>