Complete API documentation for MPFitLib public surface

[Copilot]

Two documentation gaps remained in the GH-40 branch: mp_par.cs had no XML doc comments at all, and both Solve overloads in MPFit.cs had an empty <param name="config"> tag.

Changes

• mp_par.cs — Replaced all /* */ inline comments with XML /// documentation, consistent with the rest of the public API:

  • <list type="bullet"> for the side field's five valid values
  • <remarks> + <see cref="side"/> cross-reference on deriv_debug
  • <see langword="null"/> on the nullable parname field

• MPFit.cs — Filled the empty config param doc on both Solve(mp_func, ...) and Solve(mp_func_ref, ...) overloads:

/// <param name="config">
/// pointer to structure which specifies the configuration of MPFit.Solve; or
/// <see langword="null"/> if the default configuration is to be used.
/// See <see cref="mp_config"/> for definition and use of config.
/// </param>