Format simulation results in simulations/missing-data-benchmarks

[PhilBoileau]

Simulation results are currently aggregated in the eval_results.rds files found in the bottom-level directories of the simulations/missing-data-benchmarks/results directory. The non-aggregated simulation results used to compute these summaries are not currently available due to file size constraints. This limits users ability to summarize the simulation study as best they see fit. Formatted tables containing method-specific results for each simulation replicate that respect GitHub's file size limits would solve this issue.