Fix obscure pickling bug affecting Python 3.11

[rjgildea]

This primarily affected multiprocessing in dials.integrate on Windows using Python 3.11.

The Executor base class is defined in C++ with .enable_pickling to enable lightweight pickle support. This is then subclassed e.g. for the IntegratorExecutor class, where a __getinitargs__() method is defined to provide support for pickling. For Python <= 3.10 this works just fine. However, bpo-26579 adds a default object.__getstate__() method in Python 3.11 which then triggers the Incomplete pickle support (__getstate_manages_dict__ not set) error message in Boost.Python. Adding __getstate_manages_dict__ = 1 to these subclasses appears to workaround the problem.

For example, the code print(f"{executor.__getstate__=}") on python 3.11 gives:

executor.__getstate__=<built-in method __getstate__ of IntegratorExecutor object at 0x7f52eefbf9c0>

while on python 3.10 raises an AttributeError:

AttributeError: Please report this error to dials-support@lists.sourceforge.net: 'IntegratorExecutor' object has no attribute '__getstate__'. Did you mean: '__setattr__'?

[codecov]

Codecov Report

Merging #2426 (c8200c9) into main (9cbc1e7) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head c8200c9 differs from pull request most recent head 818e5db. Consider uploading reports for the commit 818e5db to get more accurate results

@@            Coverage Diff             @@
##             main    #2426      +/-   ##
==========================================
- Coverage   78.61%   78.59%   -0.03%     
==========================================
  Files         603      604       +1     
  Lines       73927    73949      +22     
  Branches    10070    10070              
==========================================
+ Hits        58116    58118       +2     
- Misses      13671    13690      +19     
- Partials     2140     2141       +1