Adds a pure javascript implementation of trace contexts

[maraisr]

Ive built and published an NPM (and soon deno, jsr) library for dealing with trace contexts. Was originally built as a backing plane for my tracer rian, but think this can be useful for many more people.

I am also running your test harness level 2:

w3c validation test ✅

https://github.com/maraisr/tctx/blob/c4d62510034ae584a111389df878169fb30f249a/validation/test.sh#L16-L17

Im a mega fan of this spec, and love seeing where its going.