docs: show nogil in most examples (#5770)

Created using [mini-swe-agent](https://mini-swe-agent.com) and the propmt:

I'd like to find usages of PYBIND11_MODULE in the docs folder and add py::mod_gil_not_used() as a third argument if there ar
e only two arguments. These are examples, and it's really a good idea to always include that now.

I removed a few of the changes.

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
9 files changed