chore: perfectly forward all make_iterator args

[Skylion007]

Description

This forwards all args in make_iterator. This should be more efficient and allow downstream functions to use the rvalue / lvalue nature of the args).

• I also added a missing move argument and emplace_back for an lambda.

Suggested changelog entry:

* Perfect forward all args of make_iterator.

[rwgk]

To explain my rationale, in contrast to PR #3970: here you are just inserting a few && and std::move(), and use emplace_back() instead of push_back(). If we lose any of those, optimizations again, so be it.

In PR #3970, you are adding new functions and member functions. That's clearly a level up in terms of code complexity, and there is also more danger that overloads get lost unnoticed. I want to maintain a quality standard that includes: if an entire (member) function is removed accidentally, we need to see test breakages.

[henryiii]

FYI, I think this change is causing ambiguous resolution:

In file included from /Users/henryschreiner/git/scikit-hep/boost-histogram/src/register_axis.cpp:10:
/Users/henryschreiner/git/scikit-hep/boost-histogram/include/bh_python/register_axis.hpp:252:24: error: call to 'make_iterator' is ambiguous
return py::make_iterator(begin, end);
^~~~~~~~~~~~~~~~~
/Users/henryschreiner/git/scikit-hep/boost-histogram/src/register_axis.cpp:22:19: note: in instantiation of function template specialization 'register_axis<boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<0>>>' requested here
auto ax = register_axis<T>(mod);
^
/Users/henryschreiner/git/scikit-hep/boost-histogram/src/register_axis.cpp:28:5: note: in instantiation of function template specialization 'register_axis_each<boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<0>>, boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<1>>, boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<2>>, boost::histogram::axis::regular<double, boost::use_default, metadata_t>, boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<11>>, boost::histogram::axis::regular<double, boost::use_default, metadata_t, boost::histogram::axis::option::bitset<6>>, axis::regular_numpy, (lambda at /Users/henryschreiner/git/scikit-hep/boost-histogram/src/register_axis.cpp:34:50)>' requested here
register_axis_each<axis::regular_none,
^
/Users/henryschreiner/git/scikit-hep/boost-histogram/extern/pybind11/include/pybind11/pybind11.h:2373:10: note: candidate function [with Policy = pybind11::return_value_policy::reference_internal, Iterator = iterator &, Sentinel = iterator &, ValueType = pybind11::tuple, Extra = <>]
iterator make_iterator(Iterator &&first, Sentinel &&last, Extra &&...extra) {
^
/Users/henryschreiner/git/scikit-hep/boost-histogram/extern/pybind11/include/pybind11/pybind11.h:2425:10: note: candidate function [with Policy = pybind11::return_value_policy::reference_internal, Type = iterator, Extra = <iterator &>]
iterator make_iterator(Type &value, Extra &&...extra) {
^

I can fix it by adding a std::move, but I'd think that shouldn't be required to avoid ambiguity.