[Pkg-rust-maintainers] Bug#1117619: rust-hashbrown: please upgrade to v0.16

[Peter Green]

I've prepared updates for rust-hashbrown and it's dependency
rust-foldhash and uploaded them to experimental. I've also
adapted all the rust team packages that depend on them
except rust-sqlx-core (which depends on rustls)

Three of your packages btm, hx and rust-rustls depend on
rust-hashbrown and/or rust-foldhash, please can you
prepare updates for them and tell me when you are ready
for an upload to unstable.