Currently the top-level `Cargo.toml` lists members both explicitly
(direct naming) and implicitly (using globs). The latter is annoying,
and makes it hard to tell what the actual packages in the workspace are,
particularly with the complex `cargo --workspace --exclude` invocations
in CI.

This commit makes all the member explicit and puts them in alphabetical
order.

Because they don't work without OptiX, which is less important than CUDA
and a pain to install.

This means we don't have to manually exclude all these crates in CI,
which is nice -- e.g. a vanilla `cargo build` works.

Also, on Linux CI we don't need `--exclude "cudnn*"`. (We still need it
on Windows CI.)