Refactor MatchWords indexing and introduce seed indexing

Corrects the indexing strategy for seed searching, improving performance and introducing a new seed index structure for efficient pattern lookup.

This commit updates the core matching logic by shifting the indexing strategy to use two halves of k/2 bases, resulting in significant speed improvements for sequence matching. It also introduces a new `seedIndex` structure for fast pattern retrieval and implements comprehensive performance testing logic for matching functions. Future features, such as bit-parallel search, are deferred.

pkg/obiprimer/pairs_test.go

@@ -136,7 +136,7 @@ func TestPairsAgainstEcoPrimers(t *testing.T) {
 			for i, w := range sw.Words {
 				words[i] = w.Kmer
 			}
-			wm, err := matchApat(corpus, words, MatchParams{K: 18, MaxErrors: 3, Circular: true})
+			wm, err := MatchWords(corpus, words, MatchParams{K: 18, MaxErrors: 3, Circular: true})
 			if err != nil {
 				t.Fatal(err)
 			}