Improve lazy proxy typing

[thepaperpilot]

Remaining work would be:

• Update every other feature, and any relevant utilities (like in common.tsx)
• Implement processComputable, or remove it since it might just be redundant now
• Remember to delete the example achievement below the constructor, that I was using to verify typing was working
• This code doesn't work, because feature gets typed as object:

function myFeature() {
    return createLazyProxy(() => {
        const foo = "bar";
        const points = createAchievement(() => ({

        }));
        return {
            foo, points
        };
    });
}

const feature = myFeature();
feature;
feature.foo;
feature.points;

Fixes #15