Refactor

[auggiemarignier]

A suggested refactoring of the code.

• Creates a generic OneDModel class that can take any combination of rho, vp, vs, qkappa, qmu polynomial coefficients and breakpoints.
  • If a set of coefficients is not provided then if the user tries to access the related polynomial an error will be thrown. Previously, since default PREM values are given, a user could give a non-prem vp and the resulting object would still have a prem rho, which could be a problem.
  • a PREM instance of OneDModel is made available to import
• Vectorises the evaluation of piecewise polynomials at point x
• Pulls out all the calculations of physical quantities into their own physics module. These are now only functions of the five basic polynomials - no more precompute of derived polynomials so this may be an inefficiency for some applications. OneDModel contains thin wrappers around these functions so the API doesn't change from a user's perspective.
• Setup managed with uv, files rearranged into src and notebooks folders

[andreww]

These look really useful. Thanks. I'll grab and merge a bunch of these but skip the vectorisation of PP and deduplication of tabulation. My feeling is both need more test cases (or at least, for me to think about what isn't currently tested).

[andreww]

Thanks @auggiemarignier! I've merged almost all of this on main now. The missing bits are on #23 (vectorise PP) and #24 (sort out the tabulation). Both look good but would benefit from a test or two and I would really like to get my head around the vectorisation. I'll close this PR.