GeezerVison

Add primitives for x in b / x not in b where b is bytes and x is int or bytes.

Previously these used PySequence_Contains. For a bytes item that is particularly slow, since bytes.__contains__ first tries to convert the item to an integer, which raises and clears a TypeError, and then acquires a buffer.

• int in bytes: for an exact bytes object, a range check followed by memchr. Out-of-range values raise the same ValueError as CPython.
• bytes in bytes: if both are exact bytes objects and the needle is at most 32 bytes long, search directly using memchr + memcmp. Longer needles fall back to the generic implementation, which has better worst-case behavior.
• Subclasses (which may override __contains__) use the generic path.

Tests compare the results against the generic implementation (through Any) for all byte values, out-of-range and big ints, and all substrings (plus near-miss variants) of several haystacks.

Micro-benchmark (compiled code, before -> after, Python 3.13):

• int in bytes (3.2M checks): 0.025s -> 0.0086s
• 1-byte bytes in bytes (3.2M checks): 0.49s -> 0.026s
• multi-byte bytes in bytes (3.2M checks): 0.49s -> 0.039s

Part of mypyc/mypyc#644.