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GH-43748: [R] Handle package_version in safe_r_metadata (#43895)

### Rationale for this change

See #43748. There is what appears to be a bug in R's
`[[.numeric_version` implementation that leads to infinite recursion.

Edit: after some digging in R source, this appears to be as designed.
And other list subclasses that have methods to make them behave like
atomic types, like `POSIXlt`, also have this.

### What changes are included in this PR?

When recursing into list objects, `unclass()` them first to get the raw
list behavior. Also apply the checking to the `attributes()` before
reapplying them.

### Are these changes tested?

yes

### Are there any user-facing changes?

Fewer bugs!

* GitHub Issue: #43748