Init cargo deny

[future-highway]

I'd like to get cargo deny passing and to have a check in CI to make sure it remains so.

The deny.toml file was generated via cargo deny init plus a few edits:

• Added MIT and Apache 2.0 to allowed licenses
• Set confidence-threshold to 1.0 (we would need manually ok anything else)
• Set copyleft to deny

We currently do not pass the licenses check with only MIT and Apache. We also don't pass the advisories check.

[dmah42]

do you want to merge this as is, or do you want to first get us passing?