bump rand to 0.9.0-beta.3; renamed "gen" to "random"; test bigrand; fix test lints

[bionicles]

just went through and applied clippy suggestions

[bionicles]

i increased the minor version of the rand dependency
renamed "gen" to "random" in bigrand (note: this will be a breaking change, but it's necessary because of the new gen keyword being reserved)
refactored the implementations to match the updated trait
added basic tests for rand feature working (inside bigrand.rs module)

[cuviper]

If you want me to consider the clippy fixes now, please keep that in a distinct PR. Doing too much in one PR is a pretty sure way to make sure none of it gets pulled in -- especially for a first-time contributor.

The rand stuff is a breaking change even if you hadn't changed any names, because that's a public dependency. I also already have my own local branch for this upgrade, but I will wait for the proper rand 0.9.0.

[bionicles]

ok, not sure how to split up a PR, ill look into it, my bad