fix: add py::mod_gil_used() spelling, support pedantic tests (#5797)

* tests: add linking warnings/error

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

* tests: check pedantic C++14

* fix: some pedantic warnings

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

* feat: add py::mod_gil_used()

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

* fix: use not_supported()

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

* style: pre-commit fixes

* Update CMakeLists.txt

* fix: remove the true/false parameter from mod_gil_not_used

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

* style: pre-commit fixes

* Update tests/CMakeLists.txt

* fix: deprecate mod_gil_not_used(bool) instead of removing it

Keep the bool constructor public and mark it deprecated, so existing
code that spells mod_gil_not_used(false) still compiles. mod_gil_used()
now sets the flag through its friendship, which keeps the deprecated
constructor the only bool overload and stops pybind11 warning against
itself.

Also use the py:: alias in exo_planet_pybind11.cpp to match its sibling
home_planet_very_lonely_traveler.cpp.

Assisted-by: ClaudeCode:claude-opus-5

* fix: add trailing comma to macros picked up in rebase

test_smart_ptr.cpp and standalone_enum_module.cpp came from master after
this branch was written, so they still invoked variadic macros with no
variadic argument. That is a pedantic error below C++20.

Assisted-by: ClaudeCode:claude-opus-5

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/standalone_enum_module.cpp

@@ -8,6 +8,6 @@ enum SomeEnum {};
 
 using namespace standalone_enum_module_ns;
 
-PYBIND11_MODULE(standalone_enum_module, m) { // Added in PR #6015
+PYBIND11_MODULE(standalone_enum_module, m, pybind11::mod_gil_used()) { // Added in PR #6015
     pybind11::enum_<SomeEnum> some_enum_wrapper(m, "SomeEnum");
 }