Supporting older glibc versions

[ThetaSinner]

At the moment we have binaries built with Nix that are using whatever version of glibc that Nix is currently providing. That's great if you're running on a recent Linux distro which has a compatible glibc. So for example, the binaries currently run on Ubuntu 24.04 onwards.

We also have bundles built by Nix. These are self-extracting binaries that should run really widely because they bundle Nix dependencies. They are a little untidy because they unpack into /tmp and are slow on first start.

Consider how we can widen platform support without the issues of self-extracting binaries.

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@ThetaSinner I'd prefer not to build outside of Nix as well as building in Nix. If possible, I'd like a solution that doesn't require maintaining two build systems for the binaries. However, Nix doesn't really support swapping out glibc in any well-documented ways. None of the ways I've tried have worked. So that might be the best option.