gh-75459: Doc: C API: Improve object life cycle documentation#125962

  * Add "cyclic isolate" to the glossary.  * Add a new "Object Life Cycle" page.    * Illustrate the order of life cycle functions.    * Document `PyObject_CallFinalizer` and      `PyObject_CallFinalizerFromDealloc`.  * `PyObject_Init` does not call `tp_init`.  * `PyObject_New`:    * also initializes the memory    * does not call `tp_alloc`, `tp_new`, or `tp_init`    * should not be used for GC-enabled objects    * memory must be freed by `PyObject_Free`  * `PyObject_GC_New` memory must be freed by `PyObject_GC_Del`.  * Warn that garbage collector functions can be called from any    thread.  * `tp_finalize` and `tp_clear`:    * Only called when there's a cyclic isolate.    * Only one object in the cyclic isolate is finalized/cleared at a      time.    * Clearly warn that they might not be called.    * They can optionally be manually called from `tp_dealloc` (via      `PyObject_CallFinalizerFromDealloc` in the case of      `tp_finalize`).  * `tp_finalize`:    * Reference `object.__del__`.    * The finalizer can resurrect the object.    * Suggest `PyErr_GetRaisedException` and      `PyErr_SetRaisedException` instead of the deprecated      `PyErr_Fetch` and `PyErr_Restore` functions.    * Add links to `PyErr_GetRaisedException` and      `PyErr_SetRaisedException`.    * Suggest using `PyErr_WriteUnraisable` if an exception is raised      during finalization.    * Rename the example function from `local_finalize` to      `foo_finalize` for consistency with the `tp_dealloc`      documentation and as a hint that the name isn't special.    * Minor wording and sylistic tweaks.    * Warn that `tp_finalize` can be called during shutdown.