Issue #25349: Optimize bytes % args using the new private _PyBytesWriter API

* Thanks to the _PyBytesWriter API, output smaller than 512 bytes are allocated
  on the stack and so avoid calling _PyBytes_Resize(). Because of that, change
  the default buffer size to fmtcnt instead of fmtcnt+100.
* Rely on _PyBytesWriter algorithm to overallocate the buffer instead of using
  a custom code. For example, _PyBytesWriter uses a different overallocation
  factor (25% or 50%) depending on the platform to get best performances.
* Disable overallocation for the last write.
* Replace C loops to fill characters with memset()
* Add also many comments to _PyBytes_Format()
* Remove unused FORMATBUFLEN constant
* Avoid the creation of a temporary bytes object when formatting a floating
  point number (when no custom formatting option is used)
* Fix also reference leaks on error handling
* Use Py_MEMCPY() to copy bytes between two formatters (%)

Misc/NEWS

@@ -10,6 +10,8 @@ Release date: XXXX-XX-XX
 Core and Builtins
 -----------------
 
+- Issue #25349: Optimize bytes % args using the new private _PyBytesWriter API.
+
 - Issue #24806: Prevent builtin types that are not allowed to be subclassed from
   being subclassed through multiple inheritance.