json: fix option sumtype handling

[felipensp]

Fix #20181

import json

type Prices = []Price | Price

pub struct ShopResponseData {
    attributes Attributes
}

struct Attributes {
    price ?Prices
}

struct Price {
    net f64
}

fn main() {
    data := '{"attributes": {"price": [{"net": 1, "_type": "Price"}, {"net": 2, "_type": "Price"}]}}'
    entity := json.decode(ShopResponseData, data) or { panic(err) }

    data2 := '{"attributes": {"price": {"net": 1, "_type": "Price"}}}'
    entity2 := json.decode(ShopResponseData, data2) or { panic(err) }


	data3 := json.encode(ShopResponseData{attributes: Attributes{price: Prices([Price{net:1.2}])}})
	println(data3)
	entity3 := json.decode(ShopResponseData, data3) or { panic(err) }
	println(entity3)

    println(entity)
    println(entity2)
	
}

🤖[deprecated] Generated by Copilot at f83790b

Improve and fix json_no_inline_sumtypes flag for sumtypes. Add support for option sumtypes and struct variants in vlib/v/gen/c/json.v.

🤖[deprecated] Generated by Copilot at f83790b

• Fix bug and simplify code for encoding sumtypes with json_no_inline_sumtypes flag by removing unnecessary else branch (link)
• Use var_data variable instead of val prefix for encoding sumtype variants that are time.Time or other structs to make code more consistent and avoid errors (link)
• Add branch to handle decoding option sumtypes with json_no_inline_sumtypes flag by wrapping variant value in _option_ok call (link)
• Check JSON value type when decoding sumtype variants that are structs and return appropriate type and option wrapping (link, link)