[ruby] Use Rack::Utils.escape_html for escaping

[p8]

Rack::Utils.escape_html is faster than CGI.escape_html:

require 'benchmark/ips'
require 'cgi'
require 'rack'

Benchmark.ips do |x|
  x.config(warmup: 2, time: 5)

  message = 'Additional fortune added at request time.'
  x.report("CGI") do
    CGI.escape_html(message)
  end

  x.report("Rack") do
    Rack::Utils.escape_html(message)
  end

  x.compare!
end

ruby 3.4.4 (2025-05-14 revision a38531fd3f) +PRISM [arm64-darwin24]
Warming up --------------------------------------
                 CGI     1.016M i/100ms
                Rack     1.586M i/100ms
Calculating -------------------------------------
                 CGI     10.821M (± 0.3%) i/s   (92.42 ns/i) -     54.837M in   5.067830s
                Rack     15.861M (± 0.3%) i/s   (63.05 ns/i) -     80.886M in   5.099606s

Comparison:
                Rack: 15861352.0 i/s
                 CGI: 10820753.9 i/s - 1.47x  slower