Various UB warnings found by UBSan

Bug report

Bug description:

These were all found by UBSan in our CI (it just hasn't been complaining about them). They need to be individually checked, some may be false positives.

# Objects/object.c:97:5: runtime error: member access within null pointer of type 'PyThreadState' (aka 'struct _ts')
null:Objects/object.c

In test_memoryview:

# Objects/memoryobject.c:3032:15: runtime error: load of value 2, which is not a valid value for type 'bool'
bool:Objects/memoryobject.c

In test_ctypes:

# Modules/_ctypes/cfield.c:644:1: runtime error: left shift of 1 by 63 places cannot be represented in type 'int64_t' (aka 'long')
shift-base:Modules/_ctypes/cfield.c

# Modules/_ctypes/cfield.c:640:1: runtime error: signed integer overflow: -2147483648 - 1 cannot be represented in type 'int'
signed-integer-overflow:Modules/_ctypes/cfield.c

In test_zstd:

# Modules/_zstd/decompressor.c:598:56: runtime error: applying non-zero offset 18446744073709551615 to null pointer
pointer-overflow:Modules/_zstd/decompressor.c

# Modules/_io/stringio.c:350:24: runtime error: addition of unsigned offset to 0x7fd01ec25850 overflowed to 0x7fd01ec2584c
pointer-overflow:Modules/_io/stringio.c

# Objects/bytesobject.c:1190:25: runtime error: applying zero offset to null pointer
pointer-overflow:Objects/bytesobject.c

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-151274
• gh-148168
• gh-153187
• gh-153204
• gh-153258
• gh-153644
• gh-153645
• gh-154912
• gh-154913
• gh-154915
• gh-154926

Bắt đầu bằng việc xem xét các báo cáo UBSan và các vị trí được nêu trong Objects/object.c, Objects/memoryobject.c, Modules/_ctypes/cfield.c, Modules/_zstd/decompressor.c, Modules/_io/stringio.c và Objects/bytesobject.c. Chạy các bài kiểm thử CI UBSan liên quan, sau đó xác định cảnh báo nào là hợp lệ hoặc là false positive, và xác minh rằng từng cảnh báo đã được xử lý. Các PR được liên kết cho biết công việc đã được tiến hành.