Update the PATH environment variable to be able to run solidity tests…

[philippecamacho]

I made this PR because I was not able to run the solidity tests using nix. The problem was that the diff-test executable was not in the PATH environment variable.

This PR:

Update the PATH environment variable in flake.nix so that the diff-test executable can be found.

Key places to review:

flake.nix file.

[sveitser]

I think we should avoid this because it leads to cases where one may compile with "release" expecting to run these binaries but due to PATH settings one will still run the debug binaries. Or worse, if some binaries are available on debug and some only on release profile it will just pick up whatever it finds first.

I think we don't need to compile diff test with release or is it too slow with dev or test profile? We now have some optimizations for these profiles too so I think it should be fine.

[sveitser]

See other comment

[sveitser]

I think we can change the just file recipes to build the diff test binary to cargo build --profile test --bin diff-test

[philippecamacho]

I think we can change the just file recipes to build the diff test binary to cargo build --profile test --bin diff-test

Yes, it works. Done in af6c8c4.