Clarify hasTensPosition variable usage in read function

Renamed and refactored the variable `len > 1` to `hasTensPosition` for improved readability and intent clarity. Updated its usage across the function to enhance maintainability without changing the existing behavior.

Author: hckhanh

src/read/three-digits.ts

@@ -60,8 +60,9 @@ function readThreeDigitsCore(group: string): string {
     return result.trim()
   }
 
-  result += readTens(second, len > 1)
-  result += readOnes(last, second, len > 1)
+  const hasTensPosition = len > 1
+  result += readTens(second, hasTensPosition)
+  result += readOnes(last, second, hasTensPosition)
 
   return result.trim()
 }