Report unreachable duplicate partial-class match cases #5516

Describe the Bug

Pyrefly reports unreachable match cases for full class patterns, but not for duplicate or subsumed partial class patterns.

from typing import Any

class A:
    x: int

class B(A):
    pass

def f(x: Any) -> None:
    match x:
        case A(x=1):
            pass
        case A(x=1):  # should be unreachable
            pass

The duplicate is also not reported for a precise A subject, so this is a pre-existing reachability limitation rather than one specific to Any.

Expected behavior

The second A(x=1) case should be reported as unreachable because the first unguarded case already matches the same values.

case A(x=1) followed by case B() must remain reachable because a subclass instance may have a different x.

Additional context

• Related to detect match case branch subclass #3338.
• Current focused fix: fix: report unreachable match case after earlier sibling pattern #5515.
• fix: report unreachable match case after earlier sibling pattern #5515 keeps the partial-class no-false-positive behavior and leaves positive detection for this follow-up.