Proposals:

1. simplify vfs architecture: merge //zml/io and //zml/io/vfs. They have the same deps, and we only use //zml/io. New name: //zml/vfs

2. move vfs to top level (it becomes //vfs)

3. expose vfs and stdx to any zig user through zig fetch by adding build.zig and build.zig.zon

All of the above are no-op for current consumer of zml, they can still access vfs through zml.io.VFS

The PR also include two bug fix:

• S3: when no content length we were trying to read exactly 1M, while we should read up to 1M
• GCP: restore the commented code for parsing bucket info

Test plan:

bazel run --config=debug //examples/io:playground -- ls gs://gcp-public-data-landsat/
bazel run --config=debug //examples/io:playground -- tree s3://noaa-goes19/ABI-Flood-Day-Shapefiles/2025/08

zig build run_vfs_example -- tree s3://noaa-goes19/ABI-Flood-Day-Shapefiles/2025/08
zig build run_vfs_example -- ls gs://gcp-public-data-landsat/