reduce visibility on Rust KiwiVar method #94

Job	Run time
busted (luajit-openresty, ubuntu-latest)	50s
busted (luajit-openresty, windows-latest)	1m 34s
busted (luajit-openresty, macos-latest)	56s
busted (luajit-2.1.0-beta3, ubuntu-latest)	23s
busted (luajit-2.1.0-beta3, windows-latest)	2m 1s
busted (luajit-2.1.0-beta3, macos-latest)	1m 26s
busted (luajit-git, ubuntu-latest)	23s
busted (luajit-git, windows-latest)	1m 48s
busted (luajit-git, macos-latest)	1m 4s
busted (5.4.6, ubuntu-latest)	25s
busted (5.4.6, windows-latest)	1m 51s
busted (5.4.6, macos-latest)	57s
busted (5.1.5, ubuntu-latest)	23s
busted (5.1.5, windows-latest)	2m 4s
busted (5.1.5, macos-latest)	1m 20s
busted (5.3.6, ubuntu-latest)	47s
busted (5.3.6, windows-latest)	1m 45s
busted (5.3.6, macos-latest)	1m 1s
busted (luajit-git, ubuntu-latest, rust)	41s
finish	2s
publish	0s
	21m 41s

Provide feedback