Callback called before a method that is depended upon

The [Dependencies and Watchers](https://param.holoviz.org/user_guide/Dependencies_and_Watchers.html#dependency-specs) guide shows that you can depend on a _method_, as in the example below:

```python
import param

class D(param.Parameterized):
x = param.Number(0)

@param.depends('x', watch=True)
def cb1(self):
print(f"cb1 x={self.x}")

@param.depends('cb1', watch=True)
def cb2(self):
print(f"cb2 x={self.x}")

d = D()
d.x = 5
```

Output:
```
cb1 x=5
cb2 x=5
```

However, if you swap the declaration of `cb1` and `cb2`, `cb2` is called first while I would have expected `cb2` to always be called after `cb1`:

```python
import param

class D(param.Parameterized):
x = param.Number(0)

@param.depends('cb1', watch=True)
def cb2(self):
print(f"cb2 x={self.x}")

@param.depends('x', watch=True)
def cb1(self):
print(f"cb1 x={self.x}")

d = D()
d.x = 5
```

Output:
```
cb2 x=5
cb1 x=5
```