Minor optimization for Fractions.limit_denominator

When we construct the upper and lower candidates in limit_denominator,
the numerator and denominator are already relatively prime (and the
denominator positive) by construction, so there's no need to go through
the usual normalisation in the constructor. This saves a couple of
potentially expensive gcd calls.

Suggested by Michael Scott Asato Cuthbert in pythonGH-93477.

Lib/fractions.py

@@ -247,8 +247,8 @@ def limit_denominator(self, max_denominator=1000000):
             n, d = d, n-a*d
 
         k = (max_denominator-q0)//q1
-        bound1 = Fraction(p0+k*p1, q0+k*q1)
-        bound2 = Fraction(p1, q1)
+        bound1 = Fraction(p0+k*p1, q0+k*q1, _normalize=False)
+        bound2 = Fraction(p1, q1, _normalize=False)
         if abs(bound2 - self) <= abs(bound1-self):
             return bound2
         else: