fix: implement `DecodeScalar` for `Bytes`

[ifiokjr]

Fixes #334

[edgedb-cla[bot]]

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[ifiokjr]

@aljazerzen 20 minutes to build the nix environment seems excessive.

I'm also using nix with a similar set of dependencies and the total setup time is 2 minutes: https://github.com/ifiokjr/edgedb_codegen/actions/runs/10557862386/job/29246247502

It uses heavy caching and helps provide a faster feedback look. Are you happy for me to set up the same for this project?

[aljazerzen]

Yes it is :D Although I've just updated the toolchain and it had to rebuild the env.

Go ahead. The few requirements are:

• we want a dev shell for the toolchain defined in rust-toolchain.toml (there are people who want to use rustup),
• we want to test current (1.80 atm), minimum and beta versions.

[aljazerzen]

There is some caching set-up but it is apparently not working correctly.