Enable formatting CI job

[figi44]

Enable CI job to run clang-format on this repository.
Format source files, excluding src/eckit/contrib directory.

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.48 ⚠️

Comparison is base (51d3bf3) 62.64% compared to head (1b155a8) 62.16%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #67      +/-   ##
===========================================
- Coverage    62.64%   62.16%   -0.48%     
===========================================
  Files          779      784       +5     
  Lines        44303    44397      +94     
===========================================
- Hits         27752    27600     -152     
- Misses       16551    16797     +246     

see 18 files with indirect coverage changes

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[simondsmart]

This is mostly fine, and mostly looks good to merge it in.

However, there are some places where the formatting is a bit weird. Three in particular:

1. It looks like some lines have been combined/fomatted to be waaaay too long (especially where there are chains of || operations). We shouldn't be modifying the code to exceed our agreed line length.
2. The '=' alignment is being overzealous. In places it is nice, but in some cases where there is a really long line, it makes the rest look daft/unreadable. We really need to have a limit on how much this happens.
3. Alignment of comments is normally fine. But in particular the comments after public/private in class definitions aren't comments like the rest, and don't benefit from alignment.

[github-actions]

Private downstream CI failed.
Workflow name: private downstream ci hpc
View the logs at https://github.com/ecmwf-actions/private-downstream-ci/actions/runs/5212517468.

[figi44]

Reset to latest develop as all source files were formatted as part #70 and the formatting check now passes fine.

[github-actions]

Private downstream CI failed.
Workflow name: private downstream ci
View the logs at https://github.com/ecmwf-actions/private-downstream-ci/actions/runs/5221032381.

[github-actions]

Private downstream CI failed.
Workflow name: private downstream ci hpc
View the logs at https://github.com/ecmwf-actions/private-downstream-ci/actions/runs/5221100793.