Lint against cases where user likely intended to use constrained type variables

*Memo:

• mypy test.py
• mypy 1.18.2
• Python 3.14.0
• Windows 11

Instantiating the object of the class with the wrong syntax setting constraint types to the 2nd and 3rd arguments gets error properly as shown below:

                  # ↓↓↓↓↓↓↓↓↓↓ Wrong syntax
class MyCls[T: int, float, str]:
    num: T
    def __init__(self, x: T) -> None:
        self.num = x

# Instantiation
MyCls[int](100)
# Error

error: Type application has too few types

But only defining the class with the wrong syntax doesn't get the error as shown below so the error should occur:

                  # ↓↓↓↓↓↓↓↓↓↓ Wrong syntax
class MyCls[T: int, float, str]:
    num: T
    def __init__(self, x: T) -> None:
        self.num = x
# No error

Start by running the minimal Python 3.14 example with mypy 1.18.2 and compare diagnostics for the declaration alone versus the type application. Trace the generic type-variable and constrained-type analysis entry point, then add coverage so the standalone declaration reports the intended diagnostic without regressing valid syntax.