gh-143984: Replace optparse with argparse in Lib/test/test_decimal.py

The optparse module is deprecated since Python 3.2. This change migrates
Lib/test/test_decimal.py to use the argparse module for command line
argument parsing.

This involves:
- Importing argparse instead of optparse.
- Using ArgumentParser instead of OptionParser.
- Updating argument definitions (add_argument).
- Escaping '%' characters in help strings.
- Updating execution logic to use the argparse Namespace object.

Author: tonghuaroot

Lib/test/test_decimal.py

@@ -6028,15 +6028,16 @@ def test(arith=None, verbose=None, todo_tests=None, debug=None):
 
 
 if __name__ == '__main__':
-    import optparse
-    p = optparse.OptionParser("test_decimal.py [--debug] [{--skip | test1 [test2 [...]]}]")
-    p.add_option('--debug', '-d', action='store_true', help='shows the test number and context before each test')
-    p.add_option('--skip',  '-s', action='store_true', help='skip over 90% of the arithmetic tests')
-    (opt, args) = p.parse_args()
-
-    if opt.skip:
+    import argparse
+    parser = argparse.ArgumentParser(usage="test_decimal.py [--debug] [{--skip | test1 [test2 [...]]}]")
+    parser.add_argument('--debug', '-d', action='store_true', help='shows the test number and context before each test')
+    parser.add_argument('--skip',  '-s', action='store_true', help='skip over 90%% of the arithmetic tests')
+    parser.add_argument('tests', nargs='*', help='specific tests to run')
+    args = parser.parse_args()
+
+    if args.skip:
         test(arith=False, verbose=True)
-    elif args:
-        test(arith=True, verbose=True, todo_tests=args, debug=opt.debug)
+    elif args.tests:
+        test(arith=True, verbose=True, todo_tests=args.tests, debug=args.debug)
     else:
         test(arith=True, verbose=True)