Provides a lightweight, reference-counted cache for reading file lines from disk. It avoids loading entire buffers by using `vim.fn.readfile` and tracks per-buffer usage to free memory once all needed lines are retrieved. This pattern is directly reusable in any Neovim plugin that needs to efficiently fetch specific lines from multiple files without loading them as buffers.

A clean, encapsulated module for filesystem operations including path joining, absolute path detection, path shortening relative to cwd or home, and subpath checking (with case-insensitive support on Windows). It uses `vim.uv` for OS detection and provides a simple, portable API. This could be extracted as a standalone utility library for any Lua-based Neovim plugin needing path manipulation.

Implements functions to retrieve treesitter and LSP semantic token highlights for a given buffer and line. The `buf_get_ts_highlights` and `buf_get_lsp_highlights` functions are self-contained and could be reused in other plugins that need to apply external highlights to a line of text. The heuristic fallback for unloaded buffers is a nice touch.