Update CI image to use Ubuntu 23.10 as base

[msimberg]

Updates clang and related tools to version 16, based on ubuntu 23.10.

clang-format 16 introduces some major and some minor formatting changes. The major change is that it seems to change the indentation of multiline macros. I couldn't find a setting to change this back to the previous formatting so these changes we'll have to accept as they are. Additionally, I've chosen some hopefully reasonable values for a few new options in 15 and 16. Interestingly, there is now an option to insert (or remove) separators in integer literals. I've set the configuration to add separators every four digits for binary and hexadecimal literals as I think this makes it much easier to count the positions of the digits. For decimal literals I've set the option to "keep whatever is there". Another alternative would be every three digits but I found this makes some version literals (which are logically grouped by 100s) read a bit weirdly. Happy to change this if you prefer something else. The current option means that we can add separators as we see fit and clang-format won't change it. It's also possible to set it to "always remove separators".

clang-tidy also has some new checks. In the MoodyCamel concurrent queue it warns about bugprone assignment in if statements. I've silenced these. It also has a new check for optional access without a has_value/bool() guard. I've silenced the warning where we assert first that the optional is non-empty. I've also updated a number of accesses to the unchecked operator* since we already check for a value first, instead of using the checking and throwing value().

[msimberg]

This is ready for review though I would still like to at least briefly see if I can convince clang-format to do something different in context_posix.hpp as it creates very weird indentation in that file right now.

[aurianer]

LGTM thanks!

[biddisco]

LGTM

[msimberg]

cscs-ci run ci-on-merge