python/cpython

* use the `: pass` and `: yield` patterns for code that isn't expected to ever be executed.

* The _Call items passed to _AnyComparer are only ever of length two, so assert instead of if/else

* fix typo

* Fix bug, where stop-without-start patching dict blows up with `TypeError: 'NoneType' object is not iterable`, highlighted by lack of coverage of an except branch.

* The fix for bpo-37972 means _Call.count and _Call.index are no longer needed.

* add coverage for calling next() on a mock_open with readline.return_value set.

* __aiter__ is defined on the Mock so the one on _AsyncIterator is never called.

Replace check for whether something is a method in the mock module. The
previous version fails on PyPy, because there no method wrappers exist
(everything looks like a regular Python-defined function). Thus the
isinstance(getattr(result, '__get__', None), MethodWrapperTypes) check
returns True for any descriptor, not just methods.

This condition could also return erroneously True in CPython for
C-defined descriptors.

Instead to decide whether something is a method, just check directly
whether it's a function defined on the class. This passes all tests on
CPython and fixes the bug on PyPy.

Some of the *SetItem methods in the C API steal a reference to the
given value. This annotates the better behaved ones to assure the
reader that these are not the ones with the inconsistent behaviour.

* 📜🤖 Added by blurb_it.

* make docs consistent with signature

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

* Add DICT_UPDATE and DICT_MERGE bytecodes. Use them for ** unpacking.

* Remove BUILD_MAP_UNPACK and BUILD_MAP_UNPACK_WITH_CALL, as they are now unused.

* Update magic number for ** unpacking opcodes.

* Update dis.rst to incorporate new bytecodes.

* Add blurb entry.