Fix flate reader reset

[rchernobelskiy]

Thanks for the great lib!
Here is a small fix

[cristaloleg]

Looks like this change isn't back compatible. Do we need to change public API?

[cristaloleg]

Can you explain what this fixes and how?

[rchernobelskiy]

@cristaloleg Sorry I should have explained it in the PR.
When using wsflate.Reader, we need to Reset it for every message, right?
So the wsflate.Reset function tries to reuse the existing flate Reader, instead of calling the passed-in callback func to create a new one for each message.
But the reuse path is never taken, because the flate Reader Reset func has a different signature:
https://pkg.go.dev/compress/flate#Resetter
With the submitted fix, the type assesrtion in wsflate.Reset succeeds, and Reset() is properly invoked on the previously created flate.Reader (if present), allowing proper reuse.

Why do you think that it's not backwards compatible and requires public API change? It doesn't seem like it to me from first glance. (Edit: oh you mean change to the ReadResetter interface? Yes, I suppose there is not an easy way to get around that other than perhaps creating a new one/a new path)
One can of course work around this issue by wrapping the flate Reader in a custom type, but I think that's not the intended approach.