Fix ASCII compliance: Replace SMC² with SMC^2 in DESCRIPTION

Co-authored-by: osorensen <21175639+osorensen@users.noreply.github.com>

Author: Copilot

DESCRIPTION

@@ -10,7 +10,7 @@ Maintainer: Oystein Sorensen <oystein.sorensen.1985@gmail.com>
 Description: Provides nested sequential Monte Carlo algorithms for performing
     sequential inference in the Bayesian Mallows model, which is a widely used
     probability model for rank and preference data. The package implements the
-    SMC² (Sequential Monte Carlo Squared) algorithm for handling sequentially
+    SMC^2 (Sequential Monte Carlo Squared) algorithm for handling sequentially
     arriving rankings and pairwise preferences, including support for complete
     rankings, partial rankings, and pairwise comparisons. The methods are based
     on Sørensen (2025) <doi:10.1214/25-BA1564>.