Replace removed itemset method

[johnwparent]

Numpy 2.0 removes the itemset Python method from
the API
Switch to setting array values via direct array
interface for pybind11::object types

Mutable array access is unchecked for dimension
boundaries

Note: I tested this locally against Drake's bindings test suite, there were a few errors that seemed unrelated, so this approach may not be complete if those errors turn out to be related.

Note: I will be out for the upcoming holiday and the following day, so if edits are required prior to my return, please ping both myself and @BetsyMcPhail (thanks Betsy for offering to take this for a couple days)

Fixes RobotLocomotion/drake#21577

Description

Suggested changelog entry:

---

This change is 

[johnwparent]

cc @BetsyMcPhail
cc @jwnimmer-tri
(I can't assign reviewers)

[jwnimmer-tri]

The important test is to open a pull request in https://github.com/RobotLocomotion/drake/pulls that bumps Drake's git sha pin of pybind11 to point to this pull request, and run all of CI variations there.

[johnwparent]

The important test is to open a pull request in https://github.com/RobotLocomotion/drake/pulls that bumps Drake's git sha pin of pybind11 to point to this pull request, and run all of CI variations there.

I assume that's essentially the same change I had to make locally, change the repository, commit, and sha?

[jwnimmer-tri]

Since this is a pull request against the RobotLocomotion repository, you don't need to change the repository. Only the commit and sha256.

[johnwparent]

🤦‍♂️ Good point. PR made.

[jwnimmer-tri]

+@EricCousineau-TRI do you have time for a feature review pass on this one, please?

There are still some failures on the Drake PR, but they do not appear to be related to this PR -- rather just problems with numpy 2.x overall.

[EricCousineau-TRI]

As a follow-up, we should add NumPy >= 2 testing
Note that upstream (https://github.com/pybind/pybind11/blob/master/.github/workflows/ci.yml) does test NumPy >= 2, but does it on platforms that we disabled.

I can try to do that as follow-up

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @johnwparent)