[Reland] search model buffers for dtype as the last resort
Author: cyyever
Pull request: yes

# What does this PR do?

PR #23159 was reverted due to broken tests. However, I still feel the need to check buffers for dtype when the module was frozen by changing parameters to buffers. But now we search buffers as the last resort.  At this point, the old code would raise an exception because it tries to deference None as a tuple, so we can safely insert more checks without breaking the current behavior. The old PR fails because the buffer dtype is returned before checking module.\_\_dict\_\_ , which breaks backward compatibility.

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Comments:
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