Fix build warnings and a few assorted tweaks

[fu5ha]

This makes the repo workspace build under stable by putting the criterion real_blackbox feature under nightly feature in the benchmark crate. More convenient to develop with stable rust-analyzer that way. Also, adds a separate "deserialize" category to the benchmark which deserializes to owned types rather than partially zero-copy reader structs.

It also fixes some various warnings that existed on the code and reworks a bit of the net example to show off creating separate formula types from the actual serialize/deserialize structs.

[zakarumych]

I will merge this and add my own changes on top. Thank you for your contribution and interest in the project :)