Code Refactoring

[Radonirinaunimi]

This PR refactors the structure of the main NeoPDF crate, namely:

• moving the interpolation strategies into a new module strategy.rs
• moving all the interpolation logic into a new module interpolator.rs
• moving the ParamRange, RangeParameters, and SubGrid structs into a new module subgrid.rs

[github-actions]

🚀 Benchmark Results 🚀

Here are the results from the benchmark run.

xfxq2                   time:   [1.1254 µs 1.1266 µs 1.1283 µs]
Found 11 outliers among 100 measurements (11.00%)
  1 (1.00%) low mild
  5 (5.00%) high mild
  5 (5.00%) high severe

xfxq2s                  time:   [67.510 µs 67.732 µs 67.962 µs]
Found 8 outliers among 100 measurements (8.00%)
  3 (3.00%) high mild
  5 (5.00%) high severe

xfxq2_members           time:   [621.44 ps 621.52 ps 621.60 ps]
Found 5 outliers among 100 measurements (5.00%)
  2 (2.00%) high mild
  3 (3.00%) high severe