dont build sha2, opentelemetry, or zstd code if unused

reduces unnecessary crates being compiled. splits them
into features.

i have yet to see anyone use conduit's opentelemetry
stuff, and realistically those people who do
performance benchmarking and measurements will be
building stuff anyways so they can just enable this
feature.

Signed-off-by: strawberry <strawberry@puppygock.gay>