Add CLAUDE.md and a clang-format pre-commit hook

[caitlinross]

I keep forgetting to add a CLAUDE.md file, which would probably be useful.

Also adding a pre-commit hook that will run clang-format on any staged C/C++ files. This way those errors are caught before getting to CI. I also personally hate having a bunch of commits that are just "fixing formatting issues" so this will remind you (me) to do it. You do have to opt into it.

Added to the README:

To catch drift at commit time instead of in CI, enable the repo's pre-commit hook
(one-time, per clone):

git config core.hooksPath scripts/git-hooks

The hook runs the same clang-format --dry-run --Werror check CI does, on the staged
content of C/C++ files under src/, codes/, doc/, and tests/, and rejects the
commit with a fix-it command if anything drifts. Bypass a single commit with
git commit --no-verify.

When you have this enabled and try to commit a file that won't pass clang-format, you will get the following output:

$ git commit -am "Testing pre-commit hook"
pre-commit: staged files are not clang-format clean:
  src/modelconfig/config_compiler.cxx
pre-commit: fix with:  clang-format -i src/modelconfig/config_compiler.cxx
pre-commit: then re-stage (git add) and commit again. Bypass once with --no-verify.

If you use claude, it should handle running clang-format for you due to instructions in CLAUDE.md

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!