Add statistical analysis utilities and thermodynamic observables for MD

[Marcello-Sega]

• Add block-based statistical uncertainty estimation for correlated MD data.
• Add uncertainty-normalised error metrics (e.g. MAZE) for comparison with reference data.
• Add reusable thermodynamic observables including density, heat capacities, compressibility, thermal expansion, and enthalpy of vaporisation.
• Add unit tests for the statistical utilities and thermodynamic calculations.

[Marcello-Sega]

This is going to be the code underpinning #808

Suggested label: enhancement