Fix mclust covariance parameter counts for EEE and VVV models

[zeper-eng]

calc_fitindices.Mclust() currently counts off-diagonal covariance parameters as p * (p - 1) for EEE and VVV models.

Because covariance matrices are symmetric, the number of unique off-diagonal covariance parameters is p * (p - 1) / 2.

This inflates the reported parameter count and downstream information criteria for Models 3 and 6.

This change:

• corrects the EEE and VVV parameter-count formulas
• adds regression tests verifying that tidyLPA's reported parameter count agrees with the underlying mclust model's df

Testing:

• targeted regression tests: PASS 2 / FAIL 0
• full test suite: FAIL 0 / PASS 13
• Mplus-dependent tests were skipped locally because Mplus is not installed on my device.