refactor: split dbx package into domain files

Reorganize monolithic dbx.go and utility.go into focused files by
concern, add package doc.go, and gitignore coverage.out.

Co-authored-by: Cursor <cursoragent@cursor.com>

filter.go

@@ -0,0 +1,13 @@
+package dbx
+
+import "strings"
+
+// StringToFilter processes a string to be used as a filter in an SQL LIKE
+// statement. It replaces all spaces with % and adds % to the beginning and
+// end of the string.
+func StringToFilter(str string) string {
+	str = strings.Trim(str, "%")
+	str = strings.ReplaceAll(str, " ", "%")
+	str = "%" + str + "%"
+	return str
+}