CPython unittest assertion behavior

The reviewed behavior contract is derived from CPython 3.13.5:

Project: https://github.com/python/cpython
Source: https://github.com/python/cpython/blob/v3.13.5/Lib/unittest/case.py
Revision: v3.13.5
Pinned source URL: https://raw.githubusercontent.com/python/cpython/v3.13.5/Lib/unittest/case.py
Pinned source SHA-256: ce2499ee6f34a9e6e24f11ae1e2f02e71a3529cca03d5488f0bdcfea8d5d8481

Compatibility review also checked the same method in the official CPython
source at these supported-version tags:

v3.10.0  https://raw.githubusercontent.com/python/cpython/v3.10.0/Lib/unittest/case.py
          SHA-256 9daf46554125616b3dc9cbf68e2ad6d12c9e8380d9261aeea4a8bd07a178c3b1
v3.11.0  https://raw.githubusercontent.com/python/cpython/v3.11.0/Lib/unittest/case.py
          SHA-256 96301736f066147208ef01e3bbed2aee365d9ded11ba6ea407a998fcfd2e2b6f
v3.12.0  https://raw.githubusercontent.com/python/cpython/v3.12.0/Lib/unittest/case.py
          SHA-256 45bac6d80a4fc3a0dea8340a80681e30b263f017b4a5002cb8f489a632e0f987
v3.14.0  https://raw.githubusercontent.com/python/cpython/v3.14.0/Lib/unittest/case.py
          SHA-256 a79b422eec43c90352e25a54bce8cee106811974c8dea9405199e4caa689ffe9

TestCase.assertIsInstance(self, obj, cls, msg=None) returns normally only
when isinstance(obj, cls) is true; otherwise it raises AssertionError. The
optional message does not affect the assertion. The summary therefore refines
obj by cls only on the normal continuation and does not claim coverage of
workspace overrides. Because the failing branch reports through `self.fail`,
both arity-specific summaries require the receiver member `fail`; this is an
explicit dependency on the external TestCase owner rather than an override
claim. All five reviewed tags retain this normal-continuation and `self.fail`
contract. CPython 3.14 adds tuple-specific failure-message formatting, which
does not change the refinement or the required receiver member. The authored
pack therefore activates for CPython `>=3.10.0, <3.15.0`; release measurement
remains pinned to `=3.13.5`.

The pack also reviews the CPython `dataclasses.dataclass` decorator identity
contract from the official source:

Source: https://github.com/python/cpython/blob/v3.13.5/Lib/dataclasses.py
Pinned source URL: https://raw.githubusercontent.com/python/cpython/v3.13.5/Lib/dataclasses.py
Pinned source SHA-256: 18b8b97f6c43ece379793745dfd505ed713a4c86bc6babdcdec593101b5f4399

In CPython 3.13.5, `dataclass(cls=None, /, *, ...)` applies its wrapper to the
class for both `@dataclass` and `@dataclass(...)`. `_process_class` returns the
original class while `slots=False`; `_add_slots` constructs a replacement class
when `slots=True`. The reviewed pack therefore permits only literal boolean
factory options, rejects `slots=True` and `weakref_slot=True`, and does not
claim any generated member surface.
