Ensure all files include license headers

[krisnova]

For legal reasons we need to include the license in every file that we consider "Source Code".

Should we have a CI/CD check for this or any easy make target we can run to check/append files as needed?

[dmah42]

http://www.apache.org/dev/apply-license.html#copy-per-file

"DO I HAVE TO HAVE A COPY OF THE LICENSE IN EACH SOURCE FILE?

Only one full copy of the license is needed per distribution. See the policy."

I don't think we need to. if you want to that's fine, but Apache specifically doesn't require it (unlike more restrictive licenses).

[future-highway]

Don't know what the decision is going to be here, but since I have probably forgotten on 98% of the files I created, I went ahead and set clion to include the header on new rust files. Instructions for those interested:

1. Open Settings
2. Go to Editor -> File and Code Templates
3. Change Scheme to Project
4. In each file type expected to be used (e.g., Rust, Typescript), paste the header in the box.
5. Hit apply

I feel like there should be a way to add it on auto-format. I'll update if I find it. Nevermind it has been removed from rustfmt: rust-lang/rustfmt#5103