Allowed collapsing coordinates with `nbounds != (0, 2)`

[schlunma]

🚀 Pull Request

Description

This pull request allows collapsing coordinates with number of bounds different from 0 or 2 (e.g., mesh dimensions). For this, it first checks if self.is_contiguous() (that is just used to issue a warning during the collapsing of coordinates) raises an error before actually calling it. If it raises an error, issue a different warning and remove the bounds before continuing.

Closes #4672.

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