[TRANSFORMATION] Fixed bias detection in PagedCausalConv1d fusion (#35621)
### Details:
This pull request enhances the `PagedCausalConv1DFusion` transformation
by improving support for explicit bias addition after group convolution
and updating the related tests. The main focus is to ensure that when a
`GroupConvolution` is followed by an `Add` (bias) operation before a
`Slice`, the fusion correctly recognizes and incorporates the explicit
bias, or defaults to a scalar zero bias if none is present.
### Tickets:
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