sprintf deprecation warning on macOS for datetimemodule

[corona10]

How to reproduce

./configure --with-address-sanitizer && make

Deprecation warning

./Modules/_datetimemodule.c:1566:9: warning: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Wdeprecated-declarations]
        sprintf(freplacement, "%06d", 0);

[corona10]

cc @ned-deily @pganssle

[corona10]

I expect that the solution will not be hard, so I label the issue as easy

[pganssle]

Seems like a good sprint issue? Assuming we can detect this in the tests easily or otherwise verify the fix.

[arhadthedev]

Can PyOS_snprintf() be a drop-in replacement here? (edit: just asking, I will not take this issue).

[corona10]

Seems like a good sprint issue? Assuming we can detect this in the tests easily or otherwise verify the fix.

I will be happy if it can be used for the sprint issue. But I leave tomorrow, so some of the core dev can do it on the sprint.

[arhadthedev]

A parent issue: A duplicate of gh-101703.

[sobolevn]

Thanks a lot, @arhadthedev!

I will highly appreciate a review of #101729 :)
It seems ready to me.