1-to-1 Inputs and Outputs with matching timestamps are not considered up-to-date

A Target simply copies multiple SourceFiles into DestinationFiles that are also defined as Inputs and Outputs. A Copy task preserves timestamps (undocumented feature). Notice that 1-to-1 pairs will have matching timestamps, which may be different in different pairs. This is not good enough to skip the Target next time despite what [the docs](https://docs.microsoft.com/en-us/visualstudio/msbuild/incremental-builds?view=vs-2022) say.

Matching timestamps equal in pairs but not throughout are not considered up-to-date. Everything works if timestamps are equal everywhere.