Fix quantizers_test on Windows.

[ScottTodd]

Each call to _roundtrip was creating a file with the same name in the temp directory and the second write would fail. This gives each temp file a unique name manually.

We could also

• Close the file to allow it to be reopened
• Use other functions in tempfile to create uniquely named files, not just a directory

Sample error: FAILED sharktank\tests\types\quantizers_test.py::StaticScaledQuantizerTest::testPerTensorQuantDequant - RuntimeError: Error building parameter archive: D:\a\iree\iree\c\runtime\src\iree\base\internal\file_io.c:381: UNKNOWN; failed to open file 'C:\Users\RUNNER~1\AppData\Local\Temp\tmpejgrnsnpStaticScaledQuantizerTest\poodoo.irpa'. Full logs: https://github.com/nod-ai/sharktank/actions/runs/9509442435/job/26212392662.

References:

• https://github.com/iree-org/iree/blob/fe571e4d5efde141ec437cb4699307df67a38b9c/runtime/bindings/python/io.cc#L424-L491
• https://github.com/iree-org/iree/blob/fe571e4d5efde141ec437cb4699307df67a38b9c/runtime/src/iree/base/internal/file_io.c#L372-L382
• https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea

[ScottTodd]

Still seeing another flake in ThetaTest, reported here: https://github.com/nod-ai/sharktank/pull/43#issuecomment-2187545440