Add functions for quickly fitting tpcs

[fwimp]

This PR implements the fitting functions suggested in #77 and #78.

It adds 1 new dependency (glue) however this is a free dep as cli already depends upon it.

Parallel fitting requires purrr >= v1.1.0, however this is implemented as an optional feature rather than a full dependency.

[fwimp]

Woops, got some R CMD CHECK things to fix quickly

[fwimp]

Better now, but still 2 warnings and 2 notes:

N  checking R code for possible problems (5.2s)
   quickfit_tpc_multi: no visible binding for global variable 'data'
   quickfit_tpc_multi: no visible binding for global variable 'mods'
   Undefined global functions or variables:
     data mods
   Consider adding
     importFrom("utils", "data")
   to your NAMESPACE file.
W  checking for unstated dependencies in examples (544ms)
   'library' or 'require' call not declared from: 'ggplot2'
W  checking for unstated dependencies in 'tests' (4.9s)
   'library' or 'require' call not declared from: 'ggplot2'

Not deal-breakers for sure but those notes are usually a pain to fix. I'll have a look when I'm not travelling