hygiene, mark strtoi() parameters as nonnull
hygiene, rewrite dt_io_strpdt_ep() special portion
chore, adapt -i|--input-format argument to strptime in prchunk.006 regression ...

such that musl's strptime() implementation can cope as well.
Merge branch 'bld/musl'

* bld/musl:
  chore, adapt -i|--input-format argument to strptime in prchunk.006 regression ...
minor, check for overflowing the upper limit in strtoi_lim() in hindsight
hack, use ^ '0' to convert to and from ascii numbers
minor, reject invalid time fields, resort to date-only
minor, shave some more milliseconds off of strtoi_lim()
test, provide regression for strtoi_lim() inputs and expected outputs
Merge branch 'bug/strtoi_lim-out-of-range'

* bug/strtoi_lim-out-of-range:
  test, provide regression for strtoi_lim() inputs and expected outputs
  minor, shave some more milliseconds off of strtoi_lim()
  minor, reject invalid time fields, resort to date-only
  hack, use ^ '0' to convert to and from ascii numbers
  minor, check for overflowing the upper limit in strtoi_lim() in hindsight
  hygiene, rewrite dt_io_strpdt_ep() special portion
  hygiene, mark strtoi() parameters as nonnull