[integer] Update functions and methods for BigUInt (#59)

This pull request includes significant updates to the BigInt and BigUInt
benchmark functionalities and arithmetic operations. The changes add new
benchmark options and refactor the internal representation of BigInt
operations to use the `magnitude` attribute instead of `words`.

### Benchmark Updates:
*
[`benches/bigint/bench.mojo`](diffhunk://#diff-2a97f8dc8465f7a88d361dcee4dcb3020bd75f18a3a189e817fb9af8996bbb75R3-R35):
Added a new benchmark for floor division and updated the main function
to include options for running different benchmarks.
*
[`benches/biguint/bench.mojo`](diffhunk://#diff-34a58f6f5c1b673b01199db91a3b182f1f345caf0797cbcacadd978e96e4cc10R7-R35):
Updated the main function to include a menu for running different
benchmarks.

### Refactoring BigInt Operations:
*
[`src/decimojo/bigint/arithmetics.mojo`](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL54-R56):
Refactored the `add`, `subtract`, `multiply`, and `truncate_divide`
functions to use `magnitude.words` instead of `words` for internal
operations. This change affects how the arithmetic operations handle the
internal representation of BigInt.
[[1]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL54-R56)
[[2]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL63-R84)
[[3]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL117-R167)
[[4]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL204-R213)
[[5]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL218-R309)
[[6]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL296-R341)
[[7]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL307-R377)
[[8]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL344-R442)
[[9]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL404-R454)
[[10]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL416-R488)
[[11]](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL472-R530)

### New Functionality:
*
[`src/decimojo/bigint/arithmetics.mojo`](diffhunk://#diff-1ffcd7baf2074053c5e9680efda5d243ac5a3096ebf39049f4670a48bc0a932fL452-R509):
Added a new function `floor_divide` to perform floor division on BigInt
numbers, rounding towards negative infinity.

Author: forfudan

benches/bigint/bench.mojo

@@ -1,7 +1,35 @@
 from bench_bigint_add import main as bench_add
 from bench_bigint_truncate_divide import main as bench_truncate_divide
+from bench_bigint_floor_divide import main as bench_floor_divide
 
 
 fn main() raises:
-    bench_add()
-    bench_truncate_divide()
+    print(
+        """
+=========================================
+This is the BigInt Benchmarks
+=========================================
+1:       Add
+2:       Truncate Divide
+3:       Floor Divide
+4:       Run all benchmarks
+5:       Exit
+=========================================
+"""
+    )
+    var command = input("Type the number of the bench you want to run: ")
+    if command == "1":
+        bench_add()
+    elif command == "2":
+        bench_truncate_divide()
+    elif command == "3":
+        bench_floor_divide()
+    elif command == "4":
+        bench_add()
+        bench_truncate_divide()
+        bench_floor_divide()
+    elif command == "5":
+        return
+    else:
+        print("Invalid input")
+        main()