Patch ConnectionPool to carry semian_resource

[kirs]

I've been working on replacing references to a single global Redis connection in one of the Shopify apps with a ConnectionPool-wrapped Redis to make it thread-safe.

I found that so many spots expect to be able to call semian_resource on that connection object. And I don't think we should require those to go check out connection from a pool via @redis_pool.with { conn.semian_resource } to access semian_resource.

Instead, we could add semian_resource as an accessor on ConnectionPool for convenience.

Example of using that with Redis:

semian_resource = ::Redis.new(...).semian_resource
ConnectionPool.new(size: 5, timeout: 0, semian_resource: semian_resource) do
  ::Redis.new(...)
end

cc @byroot @danmayer for review

[casperisfine]

Any reason why you wouldn't just subclass/decorate ConnectionPool in your private code?

[kirs]

That's a great idea.