Cargo Features

unblock has no features set by default.

[dependencies]
unblock = { version = "0.6.0", features = ["mt", "lazy"] }
mt = num_cpus
lazy = once_cell

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

num_cpus mt?
once_cell lazy?