chore: disable fft functions for polynomials instantiated on Grumpkin

[maramihali]

This PR resolves #635 bberg and extend testing in polynomial_arithmetic.test.cpp. We now test all the functionality not related to FFT on both curves (Grumpkin doesn't have many roots of unity and we can't do FFTs on it). It also disables FFT related methods when the Polynomial class and methods in polynomial_arithmetic are instantiated with Grumpkin.

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