Introduce compare_sparse CLI tool to verify index consistency

Adds a new binary that validates bit-level consistency between dense and sparse K-mer index representations by sampling slots across partitions and reporting discrepancies. Refactors sibling cache matrix initialization into a centralized factory method to simplify control flow and standardize error handling. Introduces diagnostic configurations, benchmark scripts, and an ignored test case to support k-mer resolution analysis.

benchmark/transition.awk

@@ -0,0 +1,18 @@
+#!/usr/bin/awk -f
+
+/^>/ {
+    print
+    next
+}
+
+{
+    gsub(/[Aa]/, "a")
+    gsub(/[Gg]/, "A")
+    gsub(/a/, "G")
+
+    gsub(/[Cc]/, "c")
+    gsub(/[Tt]/, "C")
+    gsub(/c/, "T")
+
+    print
+}