gh-76785: Minor Improvements to "interpreters" Module

[ericsnowcurrently]

This includes adding pickle support to various classes, and small changes in the low-level _xxinterpqueues module that improve maintainability.

• Issue: [subinterpreters] PEP 554 implementation: add interpreters module #76785

[terryjreedy]

New warnings when compile on Windows. I suspect from this PR since compiled yesterday.

f:\dev\3x\Modules\_xxinterpqueuesmodule.c(753,25): warning C4477: 'fprintf' : f
ormat string '%ld' requires an argument of type 'long', but variadic argument 1
has type 'int64_t' [f:\dev\3x\PCbuild\pythoncore.vcxproj]
f:\dev\3x\Modules\_xxinterpqueuesmodule.c(761,25): warning C4477: 'fprintf' : f
ormat string '%ld' requires an argument of type 'long', but variadic argument 1
has type 'int64_t' [f:\dev\3x\PCbuild\pythoncore.vcxproj]
f:\dev\3x\Modules\_xxinterpqueuesmodule.c(761,25): warning C4477: 'fprintf' : f
ormat string '%ld' requires an argument of type 'long', but variadic argument 2
has type 'Py_ssize_t' [f:\dev\3x\PCbuild\pythoncore.vcxproj]

[ericsnowcurrently]

I'll take a look.