gh-138912: Add fast path for match class patterns without sub-patterns

[cdce8p]

Extracted from #139080. This builds on the work merged with 75d4839.

Add a fast path for match class patterns without any sub-patterns. This avoids creating a new (empty) tuple, pushing it to the stack and subsequently unpacking the tuple result from the MATCH_CLASS opcode again.

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Micro benchmarks with all specializations enabled.

Micro benchmark (bare class pattern)

from timeit import timeit
setup = """
class A:
    def __init__(self, x, y):
        self.x = x
        self.y = y
a = A(1, 2)

def f1(a):
    if isinstance(a, A):
        return True
    return False

def f2(a):
    match a:
        case A():
            return True
    return False
"""
print(f"If\t{timeit("f1(a)", setup, number=10**7)}")
print(f"Match\t{timeit("f2(a)", setup, number=10**7)}")

# Before
If      0.32616550009697676
Match   0.33599245804362

# After
If      0.3079932499676943
Match   0.2534141249489039 -24.58%

If specialization disabled, the performance improvement is even better with -40.5%.

• Issue: Performance improvements for the MATCH_CLASS opcode #138912

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