RFC: Deprecate either Decoupled or DecoupledIO?

**Type of issue**: feature request

**Impact**: API modification

**Development Phase**: proposal

**Other information**

**If the current behavior is a bug, please provide the steps to reproduce the problem:**

**What is the current behavior?**

User does something like:
```
val foo: DecoupledIO[Bar] = Decoupled(bar)
```

There is a mental burden to remember which one is `DecoupledIO` and which one is `Decoupled`, for no good reason.

**What is the expected behavior?**

User would write:
```
val foo: Decoupled[Bar] = Decoupled(bar)
```

OR

```
val foo: DecoupledIO[Bar] = DecoupledIO(bar)
```

We'd deprecate the other one for a version or so.

Similar for ReadyValids and such, I didn't do a comprehensive survey

**Please tell us about your environment:**

**What is the use case for changing the behavior?**

Less mental load for users.