Fix find_binary_in_dir to prefer true binaries over same-named non-binary files

[Copilot]

Which issue does this PR resolve?

Closes #

Description of this PR

Packages like fastfetch ship archives containing both a binary (usr/bin/fastfetch) and a bash-completion script (usr/share/bash-completion/completions/fastfetch). find_binary_in_dir returned whichever the directory walker hit first, which could be the completion file.

Fix: Instead of returning the first name-match, prefer candidates that are likely real binaries:

• bin/ ancestor check — file lives under a directory named bin
• Executable bit check (Unix) — file has +x permission
• Fallback — first name-match, preserving existing behavior for simple packages

// Before: returns first match (could be a completion script)
for entry in walker.filter_map(Result::ok) {
    if path.is_file() && fname == bin_name {
        return Some(path);
    }
}

// After: prefers likely binaries, falls back to first match
if is_likely_binary(path) {
    return Some(path);
}
if fallback.is_none() {
    fallback = Some(path);
}