Switch to Guile-JSON 3.x.
Guile-JSON 3.x is incompatible with Guile-JSON 1.x, which we relied on until now: it maps JSON dictionaries to alists (instead of hash tables), and JSON arrays to vectors (instead of lists). This commit is about adjusting all the existing code to this new mapping. * jupyter/kernels.scm (kernel-arguments): Use 'assoc-ref' instead of 'hash-ref'; pass JSON array through 'vector->list'. (relay-message, reply-html): Likewise. * jupyter/messages.scm (string->header): Likewise. * guix-jupyter-container.scm (local-eval, reply-execute-request): Likewise. * guix-jupyter-kernel.scm (reply-execute-request): Likewise. * guix-kernel/jupyter-client.scm (json->kernel): Likewise. * tests/kernels.scm: Likewise. * environment.scm (propagated-inputs): Replace GUILE-JSON with GUILE-JSON-3.