Debugger struct support

[Manyfestation]

Resolves #63 -

• The debugger now accepts JSON objects for State and declared struct params.
• It also accepts JSON arrays of objects for State[] and struct-array params.
• vars and print rebuild those params as source-shaped objects instead of exposing only lowered leaves.
• Debug metadata records param bindings as either:
  • SingleValue: one runtime stack slot
  • StructuredValue: one lowered leaf slot per flattened field

Example

cli-debugger ./vault.sil -f inspect --arg '{"amount":7,"tag":"0xbeef"}'

seen as -

Call Arguments:
  next (State) = {amount: 7, tag: 0xbeef}

The same also works in .test.json:

{
  "tests": [
    {
      "name": "inspect_state",
      "function": "inspect",
      "args": [{ "amount": 7, "tag": "0xbeef" }],
      "expect": "pass"
    }
  ]
}

How it work

JSON arg
  -> parsed into structured Expr values
  -> compiler lowers struct-like inputs into leaf values
  -> debug metadata records either one slot or many leaf slots
  -> debug session rebuilds object / object-array values from those leaf slots

It seems like it's necessary after all