feat: expose HasPrefixEntry for public use

[kelvinou01]

I was using rattler's HasPrefix to read info/has_prefix, and I couldn't unpack the HasPrefixEntry structs contained within, because it isn't pub:

let has_prefix = HasPrefix.from_str(...)?;
has_prefix.files.into_iter()
    .map(|HasPrefixEntry { relative_path, file_mode, prefix }| {
        // do stuff with relative_path, file_mode, and prefix
    }
    .collect()

I went thru src/package/mod.rs, and I don't think making HasPrefixEntry public is bad semantics. HasPrefix is pub for downstream consumption, so I think HasPrefixEntry should be as well? Correct me if I'm wrong, this is my first contrib to rattler :)

[baszalmstra]

LGTM! Thanks for contributing!