NotImplementedType is handled strangely

[svenzorgdoc]

Describe the bug
Pyright seems to handle NotImplementedType as a special case, and type narrowing and method resolving does not work correctly.

Code or Screenshots

from types import EllipsisType, NotImplementedType


def check1(val: int | str | NotImplementedType):
    if isinstance(val, int):
        print("Integer", val)
        reveal_type(val)  # pyright says: int | NotImplementedType
    print("Does not type check (which is good)", val + 2)  # But the report is incomplete


def check2(val: int | str | float):
    if isinstance(val, int):
        print("Integer", val)
        reveal_type(val)  # pyright says: int


def check3(val: int | str | EllipsisType):
    if isinstance(val, int):
        print("Integer", val)
        reveal_type(val)  # pyright says: int


def check4(val: int | NotImplementedType):
    if isinstance(val, int):
        print("Integer", val)
        reveal_type(val)  # pyright says: int | NotImplementedType
    print("Type checks (but should not)", val + 2)

VS Code extension or command-line
I ran the command line version of Pyright, version 1.5.0, with: npx pyright@latest not_implemented_test.py

The output is:

/tmp/not_implemented_test.py
  /tmp/not_implemented_test.py:7:21 - information: Type of "val" is "int | NotImplementedType"
  /tmp/not_implemented_test.py:8:22 - error: Operator "+" not supported for types "int | NotImplementedType | str" and "Literal[2]"
    Operator "+" not supported for types "str" and "Literal[2]" when expected type is "object" (reportOperatorIssue)
  /tmp/not_implemented_test.py:14:21 - information: Type of "val" is "int"
  /tmp/not_implemented_test.py:20:21 - information: Type of "val" is "int"
  /tmp/not_implemented_test.py:26:21 - information: Type of "val" is "int | NotImplementedType"
1 error, 0 warnings, 4 informations