feat: add duration and time_ago to theme #814

[jjjermiah]

closes #814

# Downloading a file
start <- proc.time()[[3]]
Sys.sleep(0.1)
elapsed <- proc.time()[[3]] - start
cli::cli_text('Downloaded {.file data.csv} in {.duration {elapsed}}')
#> Downloaded 'data.csv' in 107ms

# Processing step with relative time
last_sync <- Sys.time() - 125
cli::cli_text('Last sync: {.time_ago {last_sync}}')
#> Last sync: 2 minutes ago

# Progress completion
dt <- as.difftime(2.4, units = 'mins')
cli::cli_alert_success('Build completed without errors [{.duration {dt}}]')
#> ✔ Build completed without errors [2m 24s]

^{Created on 2026-04-22 with reprex v2.1.1}

no new dependencies, was able to use existing formatters.
i wouldve used pretty_dt but noted the issue in in this comment, i could add the missing fxn to the local env and swap out the custom transform