[decimojo][fix] Enhance round() function and improve the performance + fix sqrt()

README.md

@@ -25,8 +25,7 @@ For brevity, you can refer to it as "deci" (derived from the Latin root "decimus
 When you add `from decimojo import dm, Decimal` at the top of your script, this imports the `decimojo` module into your namespace with the shorter alias `dm` and directly imports the `Decimal` type. This is equivalent to:
 
 ```mojo
-import decimojo as dm
-from decimojo import Decimal
+from decimojo.prelude import dm, Decimal, RoundingMode
 ```
 
 ## Advantages
@@ -146,7 +145,7 @@ print(precise)  # 0.1234567890123456789012345678
 
 # Truncation to specific number of digits
 var large_num = Decimal("123456.789")
-print(truncate_to_digits(large_num, 4))  # 1235 (banker's rounded)
+print(round_to_keep_first_n_digits(large_num, 4))  # 1235 (banker's rounded)
 ```
 
 ### 4. Sign Handling and Absolute Value

benches/bench_add.mojo

@@ -3,7 +3,7 @@ Comprehensive benchmarks for Decimal addition operations.
 Compares performance against Python's decimal module.
 """
 
-from decimojo import dm, Decimal
+from decimojo.prelude import dm, Decimal, RoundingMode
 from python import Python, PythonObject
 from time import perf_counter_ns
 import time

benches/bench_divide.mojo

@@ -3,7 +3,7 @@ Comprehensive benchmarks for Decimal division operations.
 Compares performance against Python's decimal module.
 """
 
-from decimojo import dm, Decimal
+from decimojo.prelude import dm, Decimal, RoundingMode
 from python import Python, PythonObject
 from time import perf_counter_ns
 import time

benches/bench_multiply.mojo

@@ -3,7 +3,7 @@ Comprehensive benchmarks for Decimal multiplication operations.
 Compares performance against Python's decimal module.
 """
 
-from decimojo import dm, Decimal
+from decimojo.prelude import dm, Decimal, RoundingMode
 from python import Python, PythonObject
 from time import perf_counter_ns
 import time