Use faster way to get sec and nsec

[ganmacs]

Which issue(s) this PR fixes:
no

What this PR does / why we need it:

Process.clock_gettime is faster than Time.now if getting sec and nsec.
and Time.now is called in EventTime.now.
EventTime.now is called per data in parser_none and per chunk creation. so it's better to replace them with faster version's method.

def now1
  now = Process.clock_gettime(Process::CLOCK_REALTIME, :nanosecond)
  sec = now / 1_000_000_000
  nsec = now % 1_000_000_000
  [sec, nsec]
end

def now2
  t = Time.now
  sec = t.to_i
  nsec = t.nsec
  [sec, nsec]
end

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report("Time.now") do
    now2
  end

  x.report("Process.clock_gettime") do
    now1
  end
end

Warming up --------------------------------------
            Time.now   191.241k i/100ms
Process.clock_gettime
                       291.915k i/100ms
Calculating -------------------------------------
            Time.now      2.956M (± 1.9%) i/s -     14.917M in   5.047422s
Process.clock_gettime
                          5.563M (± 4.5%) i/s -     28.024M in   5.047899s

Docs Changes:

no need

Release Note:

same as title

[ganmacs]

memo: timecop's issue. travisjeffery/timecop#220

[repeatedly]

EventTime.now is called frequently so how about call Process.clock_gettime directly to reduce function call?

[ganmacs]

fixed 809af50