attr-defined error is raised when reading default value of an `InitVar` field of a dataclass

Bug Report
I wrote a code that reads the default value of an InitVar field of a dataclass and got attr-defined error from mypy==1.18.2. But cpython==3.13.3,3.12.10 does run without error and I believe it is reasonable to assume one can read default values from InitVar fields reading the reference.

To Reproduce

import dataclasses


@dataclasses.dataclass
class Foo:
    foo: int = 42
    bar: dataclasses.InitVar[int] = 42


print(Foo.foo)
print(Foo.bar)

Expected Behavior

no-error

Actual Behavior

<string>:12: error: "type[Foo]" has no attribute "bar"  [attr-defined]

Your Environment

• Mypy version used: 1.18.2, 1.17.1
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.13.3, 3.12.10

Start by running the reported dataclasses.InitVar example against mypy 1.18.2 and compare its treatment of Foo.foo and Foo.bar. Trace the dataclass and InitVar handling from the resulting attr-defined diagnostic, then add a regression test showing that reading the InitVar default is accepted and that the existing error remains for genuinely missing attributes.