fix(#3178): handle Windows paths in ignore_dirs and add .zig-cache to defaults

[Uanela]

This PR fixes a critical memory leak issue on Windows where nvim-tree.lua spawns infinite filesystem watchers when the .zig-cache/tmp folder creates temporary files during a build process. The watcher locks these files, preventing Zig from deleting them and causing memory to grow by 10-20 MB/second.

Changes

1. Added .zig-cache to default ignore_dirs - This directory contains build artifacts not under version control, similar to existing defaults like node_modules and build.

2. Fixed Windows path handling in ignore_dirs - The forward slash prefix (e.g., /node_modules) used in default ignore patterns wasn't matching Windows paths (e.g., M:\path\to\node_modules). The fix converts forward slashes to backslashes on Windows to ensure proper pattern matching.

Technical Details

The existing utils.escape_special_characters utility was not suitable for this fix as it only handles parentheses and curly braces in paths, not the fundamental path separator difference between Unix (/) and Windows (\).

The solution implements OS-specific path normalization in is_folder_ignored() by converting forward slashes to backslashes on Windows systems before pattern matching with vim.fn.match().

Testing

Tested on Windows 10 with Zig build process. The .zig-cache directory is now properly ignored, and existing defaults like node_modules now correctly match on Windows paths.

Closes #3178