Split benchmark demos into seperate crates

[Kixiron]

Currently we have a lot of "benchmarks" that aren't actually benchmarks, they're full fledged binaries. Currently we have them set up as benchmarks which forces us to add their dependencies as dev dependencies to dbsp as well as making custom feature sets just for the benchmarks. This can all be avoided by just making them crates and adding them to a workspace, changing cargo --bench ldbc-graphalytics -- ...args to cargo run ldbc-graphalytics ...args

[ryzhyk]

My next PR will introduce a workspace for a different reason, so we'll be able to build on top of that.