Fix recall metric calculation

[sungho-ham]

Goals :soccer:

• Fix recall metric error when batch size is 1

Implementation Details :construction:

https://github.com/NVIDIA-Merlin/Transformers4Rec/blob/23d5e3ba73b3d490400e45bf4feba94ed473432f/transformers4rec/torch/ranking_metric.py#L134 The squeeze() function removes all dimensions when batch size is 1. I've added dim=1 argument to keep dimension along batch.

Testing Details :mag:

Test code for error reproduction

import torch
from transformers4rec.torch import ranking_metric

ks = [1, 2]
scores = torch.tensor( [ [1,2,3], ])
labels = torch.tensor( [ [0,1,0], ])
ranking_metric.RecallAt()._metric(ks, scores, labels)

Error message

    135 rel_indices = (num_relevant != 0).nonzero().squeeze()
    136 rel_count = num_relevant[rel_indices]
--> 138 if rel_indices.shape[0] > 0:
    139     for index, k in enumerate(ks):
    140         rel_labels = topk_labels[rel_indices, : int(k)]

IndexError: tuple index out of range

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[rnyak]

rerun tests