fix: correct typos and reference errors causing runtime failures

[yzcj105]

Summary

This PR fixes 4 bugs that cause runtime errors or incorrect behavior:

• Fix typo in isMAC(): "maxunic" → "macunix" (was always returning false on macOS)
• Fix isLinux() function: Remove incorrect self parameter and use proper global function references
• Fix nvim-tree keymaps: Add missing keys. prefix for copy_absolute_path and toggle_file_info
• Fix fix-yank require path: "utils.fix-yank" → "insis.utils.fix-yank"

Fixes #39

Test Plan

All bugs were verified with Neovim v0.11.6:

1. isMAC() typo:

   :echo has("macunix")  --> 1 (correct)
   :echo has("maxunic")  --> 0 (typo - always false)
   

2. isLinux() error:

   Before: ERROR: attempt to index local 'self' (a nil value)
   After: Works correctly
   

3. nvim-tree keymaps: gy and gh keymaps now work in nvim-tree

4. fix-yank require:

   Before: module 'utils.fix-yank' not found
   After: Module loads correctly