Log format performance improvement

While doing some log format configuration, I came across this performance improvement. It is 4.61x slower to use strftime compared to iso8601(6). The output format is not identical, but close and has a small improvement that it includes offset IMO. Was wondering if this improvement is worth making a PR?

irb(main):9> time = Time.now
2025-10-10 09:28:08.27533 -0400

irb(main):10> time.strftime("%Y-%m-%dT%H:%M:%S.%6N")
"2025-10-10T09:28:08.275330"

irb(main):11> time.iso8601(6)
"2025-10-10T09:28:08.275330-04:00"

Warming up --------------------------------------
       Time#strftime   149.661k i/100ms
        Time#iso8601   668.851k i/100ms
Calculating -------------------------------------
       Time#strftime      1.459M (± 4.5%) i/s -      7.333M in   5.038060s
        Time#iso8601      6.731M (± 3.8%) i/s -     34.111M in   5.077102s

Comparison:
        Time#iso8601:  6730815.9 i/s
       Time#strftime:  1459156.6 i/s - 4.61x  (± 0.00) slower

Benchmark.ips do |x|
  time = Time.now
  x.report('Time#strftime') { time.strftime('%Y-%m-%dT%H:%M:%S.%6N') }
  x.report('Time#iso8601') { time.iso8601(6) }
  x.compare!
end

https://github.com/ruby/logger/blob/7827b54b0dd796891a508021146607076770b2fb/lib/logger/formatter.rb#L22

Start at lib/logger/formatter.rb around line 22 and review how the current timestamp format is used. Run the provided Benchmark.ips comparison, then determine whether the proposed iso8601(6) output is compatible with the logger's expected format and document the result before changing it.