Ignore infinities when fitting ImputeMean

[alaabenfatma]

Fixes the MeanImpute item in #105.

ImputeMean now skips infinite values when it fits the per-column means. Before this change, a column whose infinities all had the same sign got an infinite mean, and every NaN in that column was filled with it. After Standardize and Clip in the TabICLv2 recipe, those missing cells ended up at the clip bound, the same as the infinite values. The transform still leaves infinite values as they are, and columns with no finite values fall back to fill_value. This matches Standardize, which already ignores infinities when fitting.

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.