Check for no-std compatibility across dependencies

Check for no-std compatibility across dependencies

To ensure no-std is honored across dependencies, add a crate depending
on lightning crates supporting no-std. This should ensure any
regressions are caught. Otherwise, cargo doesn't seem to catch some
incompatibilities (e.g., f64::log10 unavailable in core) and seemingly
across other dependencies as describe here:

https://blog.dbrgn.ch/2019/12/24/testing-for-no-std-compatibility/