ExplaiNNTrunk.__init__ missing super().__init__() call

[Shreya-droid]

Bug description:
ExplaiNNTrunk fails to initialize because super().__init__() is missing
from its __init__ method, causing the following error:

AttributeError: cannot assign module before Module.init() call

To reproduce:
from grelu.model.models import ExplaiNNTrunk
t = ExplaiNNTrunk(in_len=200, channels=128, kernel_size=19)

Error:
File "grelu/model/trunks/explainn.py", line 92, in init
self.blocks = nn.ModuleList()
AttributeError: cannot assign module before Module.init() call

Expected behavior:
ExplaiNNTrunk should initialize successfully.

Fix:
In grelu/model/trunks/explainn.py, add super().__init__() as the first
line of ExplaiNNTrunk.init(), before self.channels = channels.