[Bug]: Regression tests fail intermittently in CI due to floating-point nondeterminism #313

Description

Regression tests produce inconsistent numerical results between local runs and GitHub Actions CI. The same tests pass locally but intermittently fail in CI due to small floating-point discrepancies in vibrational entropy calculations (including force/torque and combined FT matrices).

The failures are non-deterministic and vary slightly in magnitude across runs, suggesting environment-dependent numerical differences rather than a logical error in the implementation.

This behavior leads to regression mismatches in component-level and total entropy values, even when the underlying inputs and configuration are unchanged. The issue appears to be related to floating-point accumulation order, linear algebra backend differences, and/or multithreading in numerical libraries.