fuse integration: add POSIX compliance test suite

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test/fuse_integration/atime_nonlinux.go

@@ -0,0 +1,12 @@
+//go:build !linux && !windows
+
+package fuse
+
+import (
+	"syscall"
+)
+
+// getAtimeNano returns the access time in nanoseconds for non-Linux systems (macOS, BSD, etc.)
+func getAtimeNano(stat *syscall.Stat_t) int64 {
+	return stat.Atimespec.Sec*1e9 + stat.Atimespec.Nsec
+}