dev: Add CBMC support to nix devShell

[camshaft]

Problem:

The nix devShell is lacking the ability to run CBMC tests.

Solution:

Add support for running CBMC tests in the nix devShell

• Related Issues: dev: add s2n-dev Dockerfile #1887

[dougch]

Another project has done this work: https://github.com/pq-code-package/mlkem-native/tree/main/nix/cbmc