Fix OpenCV header detection for symlinked files

[Copilot]

Fix OpenCV detection when header files are symlinks (Issue #697)

Problem

The build script fails to detect OpenCV header files when they are symlinks, causing "Generating 0 modules" error. This commonly occurs with bazel builds which use symlinks for include directories.

Root Cause

The files_with_predicate function in build.rs uses DirEntry::file_type().is_file() which doesn't follow symlinks. Symlinks are treated as symlinks, not as regular files.

Solution

Changed to use Path::metadata() which follows symlinks by default, while maintaining the original code style with is_ok_and and then:

// Before (broken with symlinks)
.filter_map(|e| e.file_type().is_ok_and(|typ| typ.is_file()).then(|| e.path()))

// After (works with symlinks, same code style)
.filter_map(|e| {
    let path = e.path();
    // Use path.metadata() instead of e.file_type() to follow symlinks
    path.metadata().is_ok_and(|m| m.is_file()).then(|| path)
})

Testing

• ✅ Regular files: 6 files detected
• ✅ Symlinked files: 6 files detected (previously 0)
• ✅ Code style matches original pattern with is_ok_and + then

Impact

This fix allows opencv-rust to work with:

• Bazel builds using symlinked include directories
• Any build system creating symlinked header files
• Development setups using symlinks for multiple OpenCV versions

Fixes #697

Original prompt

Check the issue report: #697 The last comment from the reporter suggests that there is a problem detecting the OpenCV when they are symlinks. Investigate the codebase and fix this issue.

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[twistedfall]

@copilot Can you please keep the initial code style with is_ok_and + then?

[Copilot]

@copilot Can you please keep the initial code style with is_ok_and + then?

Done! Updated to use is_ok_and + then pattern while maintaining the symlink fix. The code now follows symlinks by using path.metadata() instead of e.file_type(), preserving the original code style. Commit: 2072ad2