Update flake.nix to make GHC 9.6.6 and GHC 9.8.2 available

[diegodiv]

The goal of this PR is to make Clash's flake usable with newer versions of GHC - 9.6.2 has this notorious problem where it throws an error when you output VHDL/Verilog. I enabled support for 9.6.6 and 9.8.2 in flake.nix along with updating flake.lock.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[diegodiv]

I changed the default version to GHC 9.10 for different reasons:

• It's the newest version and it is stable enough - and supported by Clash.
• We encountered some issues on other projects with older versions of GHC, especially with the interaction between clash-cores and Cabal, and directly going for GHC 9.10 solves the issue without having to resort to modifications like this one.