Mistake in simple_cycles signature

**Describe the bug**
In the signature of Graph.simple_cycles, the default argument for `output` is stated as `'epath'`, when the default is actually `'vpath'`.

**To reproduce**
```
import igraph as ig
G = ig.Graph.Full(4)
print(G.simple_cycles())
print(G.simple_cycles(output='epath')) #different
```

**Version information**
Python version 3.12.7, igraph version 0.11.9 installed via pip.

