fix(ci): address Windows test failures and timeout

- Extract inode function to platform-specific files (inode_unix.go,
  inode_windows.go) to fix syscall.Stat_t compile error on Windows
- Add skipOnWindows helper and skip Unix permission/symlink tests
  on Windows where chmod semantics differ
- Increase Windows test timeout from 10m to 20m since full test
  suite runs slower without race detector

Fixes Windows CI failures introduced when PR #904 expanded Windows
testing from smoke tests to full test suite.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -64,7 +64,7 @@ jobs:
           # Windows: full test suite, no race detector (slower on Windows)
           - os: windows-latest
             coverage: false
-            test-flags: '-v -short'
+            test-flags: '-v -short -timeout=20m'
     steps:
       - uses: actions/checkout@v6