[BUG] Missing Configuration Attributes in DefaultMambularConfig

[nwuestefeld]

The following attributes are missing in DefaultMambularConfig, yet they are required to initialize the ResidualBlock in the Mamba class:
conv_bias
AD_weight_decay
BC_layer_norm
d_conv

Instead of fetching these attributes from the configuration, the implementation always falls back to a fixed default value.

For instance, in line 33 of the Mamba class:

d_conv = getattr(config, "d_conv", 4)
Since d_conv is not defined in DefaultMambularConfig, it always defaults to 4, ignoring potential user-defined configurations.