Now that time_t is unconditionally 64-bit (signed int64_t) and the
struct timespec fields tv_sec / tv_nsec are wide enough on their own,
the explicit (uint64_t)/(int64_t)/(int) casts that used to guard the
multiplications and subtractions in *_us / *_ms / *_ns helpers are no
longer needed.  Drop them to keep the timekeeping math readable.

In the same spirit, this commit also normalises the printf-style format
specifiers and casts used to print tv_sec / tv_nsec / tv_usec values.
The prior code was a mix of "%d"/"%u"/"%ld"/"%lu"/"%lld" with matching
(int)/(unsigned long)/(long long) casts; some formats truncated time_t
on 32-bit hosts, others mismatched signedness or width.  Replace all
such cases with the portable POSIX-recommended forms:

  - tv_sec  (time_t,       signed, impl-defined width) -> %jd  + (intmax_t)
  - tv_nsec (long,         signed)                     -> %ld  (no cast)
  - tv_usec (suseconds_t / long)                       -> %ld  (no cast)

Also drop two stale `(FAR const time_t *)&ts.tv_sec` casts that are
unnecessary now that ts.tv_sec is plain time_t.

Arithmetic-cleanup files (existing scope):

  - benchmarks/cyclictest/cyclictest.c:        timediff_us()
  - benchmarks/sd_bench/sd_bench_main.c:       get_time_delta_us()
  - examples/oneshot/oneshot_main.c:           maxus computation
  - examples/watchdog/watchdog_main.c:         current_time_ms (x2)
  - industry/nxmodbus/nxmb_internal.h:         nxmb_util_clock_ms()
  - netutils/ntpclient/ntpclient.c:            timespec2ntp()
  - netutils/ptpd/ptpd.c:                      ptp_adjtime()
  - system/dd/dd_main.c:                       elapsed accounting
  - testing/drivers/drivertest/drivertest_posix_timer.c:
                                               get_timestamp()
  - testing/drivers/sd_stress/sd_stress_main.c:get_time_delta()
  - testing/sched/getprime/getprime_main.c:    elapsed accounting
  - testing/sched/pthread_mutex_perf/pthread_mutex_perf.c:
                                               timespec_avg()

Printf-format-fix files (new in this revision):

  - examples/adjtime/adjtime_main.c
  - examples/charger/charger_main.c
  - examples/netpkt/netpkt_ethercat.c
  - fsutils/mkfatfs/mkfatfs.c
  - graphics/tiff/tiff_initialize.c
  - netutils/ptpd/ptpd.c
  - nshlib/nsh_timcmds.c
  - system/coredump/coredump.c
  - system/ptpd/ptpd_main.c
  - testing/drivers/drivertest/drivertest_oneshot.c
  - testing/mm/kasantest/kasantest.c
  - testing/ostest/semtimed.c
  - testing/sched/pthread_mutex_perf/pthread_mutex_perf.c
  - testing/sched/timerjitter/timerjitter.c
  - testing/testsuites/kernel/time/cases/clock_test_clock01.c
  - testing/testsuites/kernel/time/cases/clock_test_smoke.c

No behavioural change.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>