gh-111962: Make dtoa thread-safe in `--disable-gil` builds. (#112049)

This updates `dtoa.c` to avoid using the Bigint free-list in --disable-gil builds and
to pre-computes the needed powers of 5 during interpreter initialization.

* gh-111962: Make dtoa thread-safe in `--disable-gil` builds.

This avoids using the Bigint free-list in `--disable-gil` builds
and pre-computes the needed powers of 5 during interpreter initialization.

* Fix size of cached powers of 5 array.

We need the powers of 5 up to 5**512 because we only jump straight to
underflow when the exponent is less than -512 (or larger than 308).

* Rename Py_NOGIL to Py_GIL_DISABLED

* Changes from review

* Fix assertion placement

1 files changed, 6 insertions, 0 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 95a72eb4704..20bfe1a0b75 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -820,6 +820,11 @@ pycore_interp_init(PyThreadState *tstate)
         return status;
     }
 
+    status = _PyDtoa_Init(interp);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     // The GC must be initialized before the first GC collection.
     status = _PyGC_Init(interp);
     if (_PyStatus_EXCEPTION(status)) {
@@ -1776,6 +1781,7 @@ finalize_interp_clear(PyThreadState *tstate)
     _PyXI_Fini(tstate->interp);
     _PyExc_ClearExceptionGroupType(tstate->interp);
     _Py_clear_generic_types(tstate->interp);
+    _PyDtoa_Fini(tstate->interp);
 
     /* Clear interpreter state and all thread states */
     _PyInterpreterState_Clear(tstate);