Remove atty dependency

[CryptoKrad]

Summary

• replace atty terminal checks with the standard library IsTerminal API
• remove the direct atty dependency from Cargo.toml
• keep behavior the same for stdin detection in extract and stdout color detection in grep

Why

atty is unmaintained and appears in RustSec audit output (RUSTSEC-2024-0375, RUSTSEC-2021-0145). Since this repo already requires Rust 1.88, std::io::IsTerminal is available and avoids carrying that dependency.

This is intentionally a narrow cleanup. A broader cargo audit pass still has unrelated workspace/dependency items, but this removes the direct atty warning without adding an allow-list entry.

Verification

• cargo fmt --check
• generated a temporary Cargo.lock and confirmed cargo tree -i atty no longer finds atty
• cargo test --lib --bins with a temporary local roaring 0.11.3 resolver pin because current fresh resolution selects roaring 0.11.4, which requires Rust 1.90 while the repo declares Rust 1.88
  • 364 lib tests passed, 1 ignored
  • 2 debug-tree-sitter bin tests passed
  • 12 probe bin tests passed

[buger]

Nice. Thanks!