Remove back pointer from Real to VALUE #491

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-latest 2.5	33s
ubuntu-latest 2.6	36s
ubuntu-latest 2.7	42s
ubuntu-latest 3.0	26s
ubuntu-latest 3.1	26s
ubuntu-latest 3.2	29s
ubuntu-latest 3.3	26s
ubuntu-latest 3.4	29s
ubuntu-latest debug	32s
ubuntu-latest head	28s
ubuntu-latest truffleruby	54s
ubuntu-latest truffleruby-head	58s
macos-latest 2.6	52s
macos-latest 2.7	54s
macos-latest 3.0	32s
macos-latest 3.1	26s
macos-latest 3.2	21s
macos-latest 3.3	19s
macos-latest 3.4	20s
macos-latest debug	21s
macos-latest head	19s
macos-latest truffleruby	55s
macos-latest truffleruby-head	1m 8s
macos-14 2.6	37s
macos-14 2.7	37s
macos-14 3.0	20s
macos-14 3.1	22s
macos-14 3.2	19s
macos-14 3.3	18s
macos-14 3.4	19s
macos-14 debug	24s
macos-14 head	17s
macos-14 truffleruby	50s
macos-14 truffleruby-head	50s
windows-latest 2.5	3m 26s
windows-latest 2.6	3m 36s
windows-latest 2.7	4m 41s
windows-latest 3.0	2m 58s
windows-latest 3.1	3m 2s
windows-latest 3.2	2m 42s
windows-latest 3.3	2m 54s
windows-latest 3.4	2m 48s
windows-latest head	3m 20s
windows-latest mingw	2m 40s
windows-latest mswin	2m 22s
	53m 12s

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