Add a prototype translation from Jax to Dex in Haskell

[axch]

To wit, serialize jaxprs from Python as JSON; parse them in Haskell into a new ADT modeling JAX IR; and compile to Dex SimpIR from there.

What works:

• Making the "compute the sine of an angle" jaxpr, shipping it to Dex, compiling it, and running the compiled function from Python.
• Round-tripping some more complex jaxprs (like cumsum implemented with scan) through the JSON encoding to Haskell and back.
• Unit-testing compile-and-run of some hand-constructed jaxpr ADTs from Haskell unit tests.

What doesn't work:

• Everything else!
• JAX literals currently compile to Dex scalar zeros.
• JAX->Dex compilation can't handle binary primitives (to say nothing of scan).
• Haven't tested compiling jaxprs that accept or return arrays.