ci: build individual crates

[WesleyRosenblum]

Problem:

Building the entire s2n-netbench workspace may result in different dependencies and features being enabled than building each crate individually. This can result in problems when publishing to crates.io, such as #5

Solution:

Add CI tasks to build each crate individually, similar to as was done in aws/s2n-quic#1673

Requirements / Acceptance Criteria:

If a dependency is used that causes an individual crate to be unbuildable, the CI task will fail