Bootstrap: revisit how we sample the input data

[barrettk]

Before we finalize the new bootstrap feature, I want to make sure we revisit the resample_df function, currently ported over from mrgmsic (along with 3 required helper functions).

mrgmisc files of interest:

• https://github.com/metrumresearchgroup/mrgmisc/blob/main/R/resampling_functions.R
• https://github.com/metrumresearchgroup/mrgmisc/blob/main/R/pad_left.R

As of making this issue, the core differences are:

• A different "padding" mechanism (mostly because I didnt want to pull in the Rcpp method it used, but also because the new method looked nicer).
• removed comments, a numeric check on a column (not sure why that was there), and doc changes (not all shown below)

Here is the file diff of those four functions (2 separate PNGs):

[seth127]

This is being added in https://github.com/metrumresearchgroup/bbr/pull/671 specifically here

[seth127]

@michaelmcd18 is going to look into this. He's been doing most of the recent maintenance on mrgmisc.

[barrettk]

Addressed in https://github.com/metrumresearchgroup/bbr/pull/671

• We opted to import this function from mrgmisc with no changes