[feat/precompile-internals] feat: move pybind11.h non-template definitions to pybind11-inl.h (#6136)

* feat: move pybind11.h non-template definitions to pybind11-inl.h

The headline of the split: cpp_function's make_function_record,
initialize_generic, destruct, and the 440-line dispatcher move out of
line, along with generic_type::initialize, enum_base, the function
signature generators, module cache helpers, keep_alive_impl,
get_type_override, error_already_set::what, and detail::print. The
templated initialize(), descr.h machinery, and the module/class_ API
stay in the header.

Assisted-by: ClaudeCode:claude-fable-5

* fix: drop redundant redeclarations in pybind11.h

These functions are already declared in function_record_pyobject.h,
attr.h, and type_caster_base.h; GCC 13 -Wredundant-decls rejects the
repeats.

Assisted-by: ClaudeCode:claude-fable-5

* fix: keep call_operator_delete(void*) inline in precompiled mode

It selects the aligned and sized operator delete from C++ feature macros.
The precompiled library can use a different C++ standard than the module
that allocated the object, so the deallocation must be compiled with the
module.

Assisted-by: ClaudeCode:claude-opus-5-5