FT: Fix and consolidate code in maars-lm and ols-summary

[ricfog]

General improvements:

• we should always return by default all estimates that have been computed through comp_var. Cases like this should be avoided. We can use this code to check which estimates are available in comp_var. If everything is set to FALSE, then the all available elements are returned
• there are multiple (3-5) functions that call the cli package and contain only a few lines of code. We should remove these functions and insert their code directly into the functions where they are actually used. However, before going ahead with this consolidation we should make sure that each of these functions is used only once

Clean/fix/more documentation:

• potentially change the name of the functioncheck_fn_args_summary because it is very similar to [check_fn_args](https://github.com/shamindras/maars/blob/iss-55-post-demo-fixes/R/utils-common.R#L92). Also check whether this information is correct
• add more examples in the documentation of get_summary
• get_assumptions should return a tibble
• comp_var needs more examples in its documentation
• remove the lines of code relative to stats::lm in summary.maars_lm because the corresponding output is not printed
• rename get_mms_summary_print_lm_style and do not print anything within the function. This function should only return the summary table with the significance codes

Consolidation:

• remove get_mms_rnm_cols_suff. This function was created in an old iteration of the code and is not used anymore
• remove fetch_mms_comp_var_attr. There is almost no synergy at play in this function, which currently serves as a very simple wrapper for many other functions. This only makes the dependencies between functions we need to be aware of more complicated. We should be calling those specific functions directly (up for a [short] discussion given @shamindras cares about this a lot :) )