[Feature] Pad Missing Values

[JamesHWade]

• Adds an optional argument to step_measure_input_long() to pad the measures in cases of missing values.
• Checks for missing values in values column for step_measure_output_wide() to prevent a value of missing columns for cases where pad = TRUE in step_measure_input_long()
• Cleanup tests and snapshots accordingly
• Updates CI workflows

[JamesHWade]

@topepo, I could use a second pair of eyes on these changes if you have the time. The intention was to add padding for users if they select pad = TRUE in step_measure_input_long().

PS - I'm back from parental leave, so I should have a lot more time to work on the package. Thanks for all your contributions so far!!!

[topepo]

I'll take a look at it.

I was thinking of something that might be related and added comments to #16 . If we had a vector class, it would make (hopefully fast) methods to go between the current data structure and a more rectangular structure that seems to be required for some packages that we could leverage.

Anyway, we don't have that right now so I'll review this as-is.

[JamesHWade]

I'm going to go ahead and merge this in favor so to go ahead and get started on the vector class.