Settings as a Struct (internal)

[HoneyryderChuck]

change internal representation of settings to a struct (instead of a plain hash), as it has better performance and storage capabilities.

STRUCT_SETTINGS = HTTP2::Settings.new
HASH_SETTINGS = {
  settings_header_table_size: 4096,
  settings_enable_push: 1, # enabled for servers
  settings_max_concurrent_streams: 100,
  settings_initial_window_size: 65_535,
  settings_max_frame_size: 16_384,
  settings_max_header_list_size: (2 << 30) - 1 # unlimited
}.freeze

uts "Struct size: #{ObjectSpace.memsize_of(STRUCT_SETTINGS)}"
puts "Hash size: #{ObjectSpace.memsize_of(HASH_SETTINGS)}"

Benchmark.ips do |x|
  # Configure the number of seconds used during
  # the warmup phase (default 2) and calculation phase (default 5)
  x.config(warmup: 2, time: 5)

  x.report("Struct lookup") do
    STRUCT_SETTINGS.settings_initial_window_size
  end

  x.report("Hash Lookup") do
    HASH_SETTINGS[:settings_initial_window_size]
  end

  # Compare the iterations per second of the various reports!
  x.compare!
end

Struct size: 80
Hash size: 160

ruby 4.0.6 (2026-07-14 revision 03b6d3f889) +PRISM [x86_64-darwin24]
Warming up --------------------------------------
       Struct lookup     1.928M i/100ms
         Hash Lookup     1.630M i/100ms
Calculating -------------------------------------
       Struct lookup     18.927M (± 8.6%) i/s   (52.83 ns/i) -     96.400M in   5.093237s
         Hash Lookup     16.252M (± 1.4%) i/s   (61.53 ns/i) -     81.504M in   5.015049s

Comparison:
Struct lookup: 18927000.6 i/s
  Hash Lookup: 16251855.2 i/s - 1.16x  slower

Closes #199 199