feat: infer ZigType(ZT) from SSZType (ST)

[twoeths]

Motivation

• for typescript, to define a SSZ type it's pretty simple

export const ValidatorType = {
  pubkey: BLSPubkey,
  withdrawalCredentials: Bytes32,
  effectiveBalance: UintNum64,
  slashed: Boolean,
  activationEligibilityEpoch: EpochInf,
  activationEpoch: EpochInf,
  exitEpoch: EpochInf,
  withdrawableEpoch: EpochInf,
};

based on that it uses ValueOf utility to infer Typescript type

• however for now in zig it has to define both ssz type and zig type

pub fn createContainerType(comptime ST: type, comptime ZT: type, hashFn: HashFn) type {

should be able to infer ZT from ST similar to typescript

Description

• infer zig type ZT from ST
  • each type needs to define getZigType() type and getZigTypeAlignment() usize at struct level
  • at compile time, infer zig type for parent type from child type using the 2 methods above
  • the creation of zig type becomes simpler since we drop ZT, it is now the same to typescript's with 1 extra param for hashFn

pub fn createContainerType(comptime ST: type, hashFn: HashFn) type {

• to get zig type from a SSZ type, use SSZType.getZigType(), this is struct method. This is equivalent to ValueOf() in Typescript ssz
• the implementation is mainly in ContainerType, syntax could be changed in future version of Zig remove @Type from the language, replacing it with individual type-creating builtins ziglang/zig#10710

comptime var new_fields: [ssz_struct_info.fields.len]std.builtin.Type.StructField = undefined;
    comptime var alignment: usize = 0;
    inline for (ssz_struct_info.fields, 0..) |field, i| {
        if (field.type.getZigTypeAlignment() > alignment) {
            alignment = field.type.getZigTypeAlignment();
        }
        new_fields[i] = .{
            .name = field.name,
            .type = field.type.getZigType(),
            // TODO: implement this
            .default_value = null,
            .is_comptime = false,
            .alignment = field.type.getZigTypeAlignment(),
        };
    }

    const ZT = comptime @Type(.{
        .Struct = .{
            .layout = .auto,
            .backing_integer = null,
            .fields = new_fields[0..],
            // TODO: do we need to assign this value?
            .decls = &[_]std.builtin.Type.Declaration{},
            .is_tuple = false,
        },
    });