Introduce JSON::Coder #791

Job	Run time
Ruby memcheck	1m 52s
ruby-versions / Generate Ruby versions	4s
ubuntu-latest 2.7	1m 2s
ubuntu-latest 3.0	32s
ubuntu-latest 3.1	40s
ubuntu-latest 3.2	35s
ubuntu-latest 3.3	1m 30s
ubuntu-latest 3.4	39s
ubuntu-latest head	1m 29s
ubuntu-latest jruby	2m 7s
ubuntu-latest jruby-head	1m 7s
macos-14 2.7	48s
macos-14 3.0	18s
macos-14 3.1	30s
macos-14 3.2	21s
macos-14 3.3	19s
macos-14 3.4	23s
macos-14 head	23s
macos-14 jruby	41s
macos-14 jruby-head	49s
windows-latest 2.7	3m 12s
windows-latest 3.0	2m 27s
windows-latest 3.1	2m 45s
windows-latest 3.2	2m 15s
windows-latest 3.3	2m 40s
windows-latest 3.4	2m 24s
windows-latest head	1m 25s
ubuntu-24.04-arm 3.4	42s
macos-13 3.4	34s
windows-latest mswin	1m 30s
ubuntu-latest jruby-9.4	1m 7s
macos-latest truffleruby-head	37s
ubuntu-latest truffleruby-head	2m 9s
	39m 56s

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