feat: add Fourier and vectorized Polynomial basis functions with accompanying tests.

[dhruvpal102005]

Hey! This PR adds the include_bias option to Polynomial and Fourier basis functions.

Right now, some basis functions like Legendre and Hermite already let you control whether to include a bias term, but Polynomial and Fourier didn't have that option. This was limiting for certain modeling scenarios where you might not want the bias term.

What changed:

• Added include_bias parameter to both Polynomial and Fourier
• Set the default to True to match what Legendre, Hermite, etc. are doing
• Updated the existing tests since the default behavior now includes a bias column
• Added some new tests to make sure both include_bias=True and include_bias=False work correctly

Testing:

Tested manually and everything works as expected:

• When include_bias=True, you get a column of ones prepended to the output
• When include_bias=False, no bias column is added

Let me know if you'd like me to change anything!

Fixes #193