[integer] Refine the constructors of BigUInt

benches/bigint/bench.mojo

@@ -19,7 +19,7 @@ q:           Exit
 =========================================
 """
     )
-    var command = input("Type the number of the bench you want to run: ")
+    var command = input("Type name of bench you want to run: ")
     if command == "add":
         bench_add()
     elif command == "mul":

benches/biguint/bench.mojo

@@ -1,6 +1,7 @@
 from bench_biguint_add import main as bench_add
 from bench_biguint_multiply import main as bench_multiply
 from bench_biguint_truncate_divide import main as bench_truncate_divide
+from bench_biguint_from_string import main as bench_from_string
 
 
 fn main() raises:
@@ -12,22 +13,26 @@ This is the BigUInt Benchmarks
 add:         Add
 mul:         Multiply
 trunc:       Truncate divide (//)
+fromstr:     From string
 all:         Run all benchmarks
 q:           Exit
 =========================================
 """
     )
-    var command = input("Type the number of bench you want to run: ")
+    var command = input("Type name of bench you want to run: ")
     if command == "add":
         bench_add()
     elif command == "mul":
         bench_multiply()
     elif command == "trunc":
         bench_truncate_divide()
+    elif command == "fromstr":
+        bench_from_string()
     elif command == "all":
         bench_add()
         bench_multiply()
         bench_truncate_divide()
+        bench_from_string()
     elif command == "q":
         return
     else: