feat(fs): readlink/readlinkat and correct ioctl errno

[FlareCoding]

Summary

• Running a Python script by path failed with ENOSYS because two file operations returned the wrong errno for unsupported cases, so CPython aborted the open.
• readlink/readlinkat are now implemented, returning EINVAL for non-symlinks (the POSIX answer realpath expects) instead of an unimplemented-syscall ENOSYS; real targets are read for when symlink creation later lands.
• ioctl on a request the object does not support now returns ENOTTY instead of ENOSYS, so CPython's close-on-exec probe falls back to fcntl instead of treating the open as failed. Together these let python3.12 run a file.

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