Adopt latest torchmetrics changes

[carmocca]

🚀 Feature

Adapt the _ResultMetric code to the recent changes in Lightning-AI/torchmetrics#840 to prepare for the next torchmetrics release.

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cc @carmocca @edward-io @ananthsub @rohitgr7 @kamil-kaczmarek @Raalsky @Blaizzy

[carmocca]

Closing this as the change was reverted: Lightning-AI/torchmetrics#876

cc @awaelchli @Borda @SkafteNicki