PERF: Avoid deepcopy in Series arithmetic operations

[jbrockmendel]

xref #4689

In cases such as df[0] - df[1], we have df[0].index._id is df[1].index._id, which means the .equals check in the alignment step is cheep. Making a deep copy resets the two _id objects, making the alignment much more expensive.

[pyrito]

Thanks for opening the issue @jbrockmendel

[jbrockmendel]

closed by #4689?

[mvashishtha]

@jbrockmendel yes. On your future PRs please be sure fill out the PR template. The template includes a portion for the issue like Resolves #. If you put the issue number there, GitHub will close the issue automatically once the PR is merged.