Make encoding function static #469

Job	Run time
build	8s
build	8s
Test built gem (windows, head, 15.1-1-windows-x64, 15)	6m 6s
Test built gem (windows, head, 15.1-1-windows-x64, 15)	6m 6s
Test built gem (windows, 2.5, 9.4.26-1-windows-x64, 9.4)	9m 42s
Test built gem (windows, 2.5, 9.4.26-1-windows-x64, 9.4)	9m 42s
Test built gem (ubuntu, head, 15)	1m 13s
Test built gem (ubuntu, head, 15)	1m 13s
Test built gem (ubuntu, 3.2, 12)	1m 27s
Test built gem (ubuntu, 3.2, 12)	1m 27s
Test built gem (ubuntu, 20.04, 2.5, 9.3)	1m 43s
Test built gem (ubuntu, 20.04, 2.5, 9.3)	1m 43s
Test built gem (ubuntu, truffleruby, 13)	1m 52s
Test built gem (ubuntu, truffleruby, 13)	1m 52s
Test built gem (ubuntu, truffleruby-head, 15)	3m 56s
Test built gem (ubuntu, truffleruby-head, 15)	2m 7s
Test built gem (macos, head, 15.1-1-osx, 15)	1m 47s
Test built gem (macos, head, 15.1-1-osx, 15)	1m 47s
	53m 59s

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