Introduce JSON::Coder #787

Job	Run time
Ruby memcheck	1m 2s
ruby-versions / Generate Ruby versions	2s
ubuntu-latest 2.7	1m 8s
ubuntu-latest 3.0	43s
ubuntu-latest 3.1	46s
ubuntu-latest 3.2	1m 31s
ubuntu-latest 3.3	43s
ubuntu-latest 3.4	49s
ubuntu-latest head	1m 34s
ubuntu-latest jruby	1m 11s
ubuntu-latest jruby-head	1m 11s
macos-14 2.7	56s
macos-14 3.0	26s
macos-14 3.1	28s
macos-14 3.2	22s
macos-14 3.3	25s
macos-14 3.4	28s
macos-14 head	18s
macos-14 jruby	45s
macos-14 jruby-head	42s
windows-latest 2.7	4m 54s
windows-latest 3.0	2m 51s
windows-latest 3.1	2m 39s
windows-latest 3.2	2m 15s
windows-latest 3.3	3m 43s
windows-latest 3.4	4m 0s
windows-latest head	2m 17s
ubuntu-24.04-arm 3.4	44s
macos-13 3.4	36s
windows-latest mswin	3m 30s
ubuntu-latest jruby-9.4	1m 10s
macos-latest truffleruby-head	36s
ubuntu-latest truffleruby-head	2m 9s
	46m 54s

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