Replace JSON with TOML for snapshot

But this made unparsable error for 10000+ years

May relate to toml-lang/toml#538 (comment)

Gemfile

@@ -16,6 +16,7 @@ group(:development) do
   gem('steep', '~> 1.6.0', require: false)
   gem('benchmark-ips', '~> 2.13.0', require: false)
   gem('stackprof')
+  gem('perfect_toml', '~> 0.9.0', require: false)
   gem('yard', '~> 0.9.36', require: false)
   gem('rubocop', '~> 1.61.0', require: false)
   gem('rubocop-rake', '~> 0.6.0', require: false)

_typos.toml

@@ -0,0 +1,2 @@
+[files]
+extend-exclude = ["test/many_data/fixtures"]

scripts/convert_snapshot_dump_to_toml.rb

@@ -0,0 +1,20 @@
+# coding: us-ascii
+# frozen_string_literal: true
+
+require('bundler/setup')
+require_relative('../lib/ulid')
+require_relative('../test/many_data/fixtures/example')
+
+require('perfect_toml')
+
+path_prefix = "#{__dir__}/../test/many_data/fixtures/dumped_fixed_examples_"
+timestamp = "2024-01-10_07-59"
+without_ext = "#{path_prefix}#{timestamp}"
+dump_data = File.binread("#{without_ext}.bin")
+examples = Marshal.load(dump_data)
+toml_prepared = examples.sort_by(&:integer).to_h { |example| [example.string, example.to_h.except(:string, :period) ] }
+PerfectTOML.save_file("#{without_ext}.toml", toml_prepared)
+
+if toml_prepared == PerfectTOML.load_file("#{without_ext}.toml")
+  raise 'there is a bug for serialization or deserialization in snapshots'
+end