Allow void in ok/err in custom result type

[afsalthaj]

Fixes #182

For the following agent, with rpc calls

import {
    BaseAgent,
    agent,
    WithRemoteMethods
} from '@golemcloud/golem-ts-sdk';

@agent()
class HelloAgent extends BaseAgent {
    private readonly client: WithRemoteMethods<RemoteAgent>;
    private value: number = 0;

    constructor(name: string) {
        super()
        this.client = RemoteAgent.get(name);
    }

    async foo(input: MyResult1): Promise<MyResult1> {
       return await this.client.qux(input);
    }

    async bar(input: MyResult2): Promise<MyResult2> {
        return await this.client.corge(input);
    }

    async baz(input: MyResult3): Promise<MyResult3> {
        return await this.client.grault(input);
    }
}

@agent()
class RemoteAgent extends BaseAgent {
    private readonly id: string;

    constructor(name: string) {
        super()
        this.id = name;
    }

    async qux(input: MyResult1): Promise<MyResult1> {
        return input;
    }

    async corge(input: MyResult2): Promise<MyResult2> {
        return input;
    }

    async grault(input: MyResult3): Promise<MyResult3> {
        return input
    }
}


type MyResult1 = { tag: 'ok', okVal: void } | { tag: 'err', errVal: string };
type MyResult2 = { tag: 'ok', okVal: number } | { tag: 'err', errVal: void };
type MyResult3  = { tag: 'ok', okVal: void } | { tag: 'err', errVal: void };

Manual tests:

Also, exports shows

I will be adding these as tests back in golem once released