Fix FLS FiberManager writing last_error to a dead attribute

[w1tcher]

Summary

FiberManager (qiling/os/windows/fiber.py) reports ERROR_INVALID_PARAMETER
for an invalid FLS index by writing self.last_error in free(), set() and
get(). But self.last_error is a plain attribute on the FiberManager
instance that nothing ever reads — it is written in three places and read
in none.

The Windows last-error that GetLastError returns lives on ql.os.last_error
(hook_GetLastError returns it, hook_SetLastError writes it, and every other
kernel32 hook sets errors via ql.os.last_error = ...). Because the FLS code
wrote the wrong object, FlsFree / FlsSetValue / FlsGetValue never actually
surfaced ERROR_INVALID_PARAMETER to the emulated program: a guest calling one
of these with a bad index, then GetLastError() to disambiguate the result,
would see a stale/zero error code.

Fix

Route the three writes to self.ql.os.last_error (the FiberManager already
holds self.ql), making the FLS error path consistent with the rest of
kernel32. No API surface or signature changes; 3 lines in one file.

This is independent of #1637 (which adds FlsGetValue2/get_noerr). It is worth
noting the two interact: only once the last-error actually lands on
ql.os.last_error does the intended FlsGetValue (sets error on bad index) vs
FlsGetValue2 (does not) distinction become observable to the guest.

Checklist

Which kind of PR do you create?

• This PR only contains minor fixes.
• This PR contains major feature update.
• This PR introduces a new function/api for Qiling Framework.

Coding convention?

• The new code conforms to Qiling Framework naming convention.
• The imports are arranged properly.
• Essential comments are added.
• The reference of the new code is pointed out.

Extra tests?

• No extra tests are needed for this PR.
• I have added enough tests for this PR.
• Tests will be added after some discussion and review.

Changelog?

• This PR doesn't need to update Changelog.
• Changelog will be updated after some proper review.
• Changelog has been updated in my PR.

Target branch?

• The target branch is dev branch.

One last thing

• I have read the contribution guide