gh-128213: fast path for bytes creation from list and tuple

[eendebakpt]

Continuation of #128214. This PR

• Improves performance of bytes creation from a list or tuple
• Fixes a free-threading bug
• Reduces some duplicated code between list and tuple handling

• Issue: Speed up bytes creation from list and tuple #128213

[StanFromIreland]

Suggested change

	/* Py_None as a fallback sentinel to the slow path */
	bytes = Py_None;
	/* Py_None as a fallback sentinel to the slow path */
	Py_INCREF(Py_None);
	bytes = Py_None;

Is needed, no?

[eendebakpt]

Py_None is immortal, so not needed

[markshannon]

If you're interested in speed, PyLong_CheckExact will allow you to use _PyLong_IsNonNegativeCompact and _PyLong_CompactValue to get the C int in a few cycles.

[eendebakpt]

Interesting. For the common/happy path we now we call PyNumber_AsSsize_t, which calls PyLong_AsSsize_t. That methods does another PyLong_Check and then a call to _PyLong_IsCompact.

So we have some options:

1. We could remove the call to PyLong_Check (as it is already covered by PyLong_AsSsize_t), that improves performance a bit for all cases.
2. We could use PyLong_CheckExact with _PyLong_IsNonNegativeCompact. Fastest for exact ints, but non-exact ints become slower. I suspect non-exact ints are rare though.
3. We add a fast path using PyLong_CheckExact and a fallback fast path using PyNumber_AsSsize_t for the non-exacts ints. Fast for all cases, but takes a but more code.

@markshannon Any preference? I am happy to work out any of the above.

[markshannon]

Tuples are immutable, so why does creating a bytes object from a tuple require synchronization?

[eendebakpt]

Tuples are immutable, so why does creating a bytes object from a tuple require synchronization?

Tuples indeed do not require synchronization.

In this PR exact lists and tuples use the path (using synchronization with Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST). We could split the path, but I suspect the performance gain for tuples would be minimal.