Add ATLAS metadata filesystem source

[jayvenn21]

Summary

Adds ATLAS metadata support to the FUSE filesystem.

This change loads ATLAS entries from a TSV file and exposes them through the mounted filesystem under an atlas/ directory. Each ATLAS protein entry is represented as a directory containing a metadata.json file with the row metadata serialized as JSON.

Example mounted layout:

/tmp/atlas_mount/
  atlas/
    1r6w_A/
      metadata.json

Changes

• Added TSV parsing for ATLAS metadata
• Added atlas datasource construction from loaded entries
• Added inode-to-content storage for generated JSON files
• Updated read() to serve metadata JSON contents
• Updated getattr() / lookup behavior so generated files report correct sizes
• Updated directory listing so ATLAS entry directories expose metadata.json
• Added README instructions for Linux/macOS setup and local TSV usage
• Ignored local TSV data files via .gitignore

Testing

Tested locally on macOS with macFUSE:

cargo check
cargo run --release -- data/2024_11_18_ATLAS_info.tsv /tmp/atlas_mount

Verified:

ls /tmp/atlas_mount
ls /tmp/atlas_mount/atlas | head
ls /tmp/atlas_mount/atlas/1r6w_A
cat /tmp/atlas_mount/atlas/1r6w_A/metadata.json

The filesystem loaded 1,938 ATLAS entries and returned JSON metadata for 1r6w_A.