fix: global workspace scheduler arg as a callback (#169)

The previous implementation (#132) could not work with new scheduler as
it could
not take the optimizer as param.
Here, the scheduler should be a callback instead:

```python
def get_scheduler(optimizer: Optimizer) -> LRScheduler:
    return StepLR(otimizer, ...)

gw = GlobalWorkspace(
        ...
        scheduler=get_scheduler
)
```

shimmer/modules/global_workspace.py

@@ -9,6 +9,7 @@
 from torch.nn import Module, ModuleDict
 from torch.optim.adamw import AdamW
 from torch.optim.lr_scheduler import LRScheduler, OneCycleLR
+from torch.optim.optimizer import Optimizer
 
 from shimmer.modules.contrastive_loss import ContrastiveLoss, ContrastiveLossType
 from shimmer.modules.domain import DomainModule, LossOutput
@@ -230,7 +231,7 @@ def __init__(
         optim_lr: float = 1e-3,
         optim_weight_decay: float = 0.0,
         scheduler_args: SchedulerArgs | None = None,
-        scheduler: LRScheduler
+        scheduler: Callable[[Optimizer], LRScheduler]
         | None
         | OneCycleSchedulerSentinel = OneCycleSchedulerSentinel.DEFAULT,
     ) -> None:
@@ -245,7 +246,8 @@ def __init__(
             optim_weight_decay (`float`): weight decay
             scheduler_args (`SchedulerArgs`): `SchedulerArgs` instance to define
                 scheduler parameters.
-            scheduler: scheduler to use. If None is explicitely given, no scheduler
+            scheduler (`Callable[[Optimizer], LRScheduler]`): Callback that returns the
+                scheduler to use. If None is explicitely given, no scheduler
                 will be used. By default, uses OneCycleScheduler
         """
         super().__init__()
@@ -604,7 +606,7 @@ def configure_optimizers(self) -> OptimizerLRScheduler:
         if isinstance(self.scheduler, OneCycleSchedulerSentinel):
             lr_scheduler = OneCycleLR(optimizer, **self.scheduler_args)
         else:
-            lr_scheduler = self.scheduler
+            lr_scheduler = self.scheduler(optimizer)
 
         return {
             "optimizer": optimizer,
@@ -661,7 +663,7 @@ def __init__(
         scheduler_args: SchedulerArgs | None = None,
         learn_logit_scale: bool = False,
         contrastive_loss: ContrastiveLossType | None = None,
-        scheduler: LRScheduler
+        scheduler: Callable[[Optimizer], LRScheduler]
         | None
         | OneCycleSchedulerSentinel = OneCycleSchedulerSentinel.DEFAULT,
         fusion_activation_fn: Callable[[torch.Tensor], torch.Tensor] = torch.tanh,
@@ -739,7 +741,7 @@ def __init__(
         scheduler_args: SchedulerArgs | None = None,
         learn_logit_scale: bool = False,
         contrastive_loss: ContrastiveLossType | None = None,
-        scheduler: LRScheduler
+        scheduler: Callable[[Optimizer], LRScheduler]
         | None
         | OneCycleSchedulerSentinel = OneCycleSchedulerSentinel.DEFAULT,
         fusion_activation_fn: Callable[[torch.Tensor], torch.Tensor] = torch.tanh,