Add log_elapsed()

[thomasp85]

This PR adds a function that works much like log_tictoc() but rather than reset the counter at each call it continues to count up

[daroczig]

Very cool, thank you! Could you pls check above typo in nolint and the R CMD check results?

[thomasp85]

Done - the failing CI was because I didn't update the docs for the quiet argument

[thomasp85]

Interesting bug in older R versions

[daroczig]

This might need a pkgdown config update to explicitly list the new fn(s).