gh-106316: Remove pytime.h header file (#106317)

Remove the "cpython/pytime.h" header file: it only contained private
functions. Move functions to the internal pycore_time.h header file.

Move tests from _testcapi to _testinternalcapi. Rename also test
methods to have the same name than tested C functions.

No longer export these functions:

* _PyTime_Add()
* _PyTime_As100Nanoseconds()
* _PyTime_FromMicrosecondsClamp()
* _PyTime_FromTimespec()
* _PyTime_FromTimeval()
* _PyTime_GetPerfCounterWithInfo()
* _PyTime_MulDiv()

Author: vstinner

.github/CODEOWNERS

@@ -79,7 +79,7 @@ Doc/library/time.rst          @pganssle @abalkin
 Lib/test/test_time.py         @pganssle @abalkin
 Modules/timemodule.c          @pganssle @abalkin
 Python/pytime.c               @pganssle @abalkin
-Include/pytime.h              @pganssle @abalkin
+Include/internal/pycore_time.h  @pganssle @abalkin
 
 # Email and related
 **/*mail*                     @python/email-team

Doc/whatsnew/3.13.rst

@@ -602,3 +602,6 @@ Removed
   use ``PyObject_Vectorcall()`` which is available since Python 3.8
   (:pep:`590`).
   (Contributed by Victor Stinner in :gh:`106023`.)
+
+* Remove ``cpython/pytime.h`` header file: it only contained private functions.
+  (Contributed by Victor Stinner in :gh:`106316`.)

Include/Python.h

@@ -83,7 +83,6 @@
 #include "weakrefobject.h"
 #include "structseq.h"
 #include "cpython/picklebufobject.h"
-#include "cpython/pytime.h"
 #include "codecs.h"
 #include "pyerrors.h"
 #include "pythread.h"

Include/cpython/pytime.h

@@ -5,6 +5,8 @@
 extern "C" {
 #endif
 
+#include "pycore_time.h"          // _PyTime_t
+
 
 struct _import_runtime_state {
     /* The builtin modules (defined in config.c). */