[BUG] Regression in CastOpSuite due to cuDF change in parsing NaN

[andygrove]

Describe the bug

cuDF commit rapidsai/cudf@69d5765 appears to have caused a regression in CastOpSuite because cuDF now supports + and - preceding Nan and Inf. There are other changes that impact the plugin as well, such as supporting mixed case (e.g. nAn) and also supporting the word Infinity in full.

- Cast from string to float using hand-picked values *** FAILED ***
  Mismatch casting string [+nAn] to FloatType. CPU: null; GPU: NaN (CastOpSuite.scala:258)

Steps/Code to reproduce bug
Run test using cuDF that includes rapidsai/cudf@69d5765

Expected behavior
Test should pass

Environment details (please complete the following information)
N/A

Additional context
N/A