Conditionally dependencies with strict version bounds

[sethaxen]

I see that InfiniteArrays only works for Julia 1.5. Is this dependency required, or can it be conditionally loaded with Requires so offer support for older Julia versions? Are there other dependencies with strict bounds that can be relaxed?

[cscherrer]

I think currently this is only for ∞. That's defined in Infinities.jl, but I think InfiniteArrays extends it. We could PR to that to move the functionality to Infinities and/or support older versions. Worst-case we could replicate only the code needed for that.

Supporting older Julia versions is a lower priority to me, but I'm open to changes in that direction as long as we're not sacrificing performance or functionality.