Add lattice rules for (hyper)cubic grid integration

[Ao-chuba]

This PR implements lattice rules for efficient numerical integration over (hyper)cubic grids, addressing issue #241 .

Following the references provided in the issue (Sloan's paper and the UNSW lattice rules database), I've implemented rank-1 lattice rules as a new integration method.
Implementation :

• New Lattice class using tabulated generating vectors from UNSW database
• Supports embedded lattice rules (powers of 2, up to 2²⁰ points)
• Equal-weight integration with formula: $\mathbf{x}_k = { \frac{k \cdot \mathbf{z}}{n} }$
• Works with arbitrary parallelepipeds via affine transformation
• Supports up to 50 dimensions (extensible to 3600+ if needed)
• Includes basic interpolation via scipy.interpolate.LinearNDInterpolator

Testing:

• Input validation, point generation, integration accuracy
• Embedded property verification, interpolation, file I/O

closes #241