feat(cli): add peer count to file download

[mickvandijke]

Summary

• add ant file download --peers <COUNT> with --peer-count alias
• thread the requested peer count through public DataMap fetches and file chunk downloads
• add parser coverage for public/private downloads and zero rejection

Tests

• cargo test -p ant-cli commands::data::file::tests::download_peers
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings