Job Queues: Improve typing for input/output schema

[tyteen4a03]

While looking at the types for an issue where date fields specified in the inputSchema does not result in a Date object being passed to the handler, I noticed the types aren't narrowed down to JSON-serializable fields (which I think is the intent, given that Payload currently turns date fields into strings in generate:types)

I think the schema should be tied down to only simple fields that can be safely JSON-serialized (e.g. what does an input with field join mean? and do we really need to let devs go ham by giving them blocks?). Maaaaybe we should give special treatment to date field where the handler gets Date objects back but I already shudder to think about the consequences of timezones and stuff, it feels like something the dev should handle themselves with their favorite datetime library.