feat: clean up `gnokey add` + add coverage #5004

Job	Run time
build (1.21.x, GOARCH=amd64 GOOS=linux, gno)	31s
build (1.21.x, GOARCH=wasm GOOS=js, gno)	26s
build (1.22.x, GOARCH=amd64 GOOS=linux, gno)	29s
test (1.21.x, _test.cmd)	1m 44s
build (1.22.x, GOARCH=wasm GOOS=js, gno)	30s
test (1.21.x, _test.pkg)	57s
test (1.21.x, _test.gnolang.native)	34s
test (1.21.x, _test.gnolang.stdlibs)	58s
test (1.21.x, _test.gnolang.realm)	34s
test (1.21.x, _test.gnolang.pkg0)	2m 9s
test (1.21.x, _test.gnolang.pkg1)	6m 28s
test (1.21.x, _test.gnolang.pkg2)	4m 11s
test (1.21.x, _test.gnolang.other)	27s
test (1.22.x, _test.cmd)	1m 41s
test (1.22.x, _test.pkg)	1m 2s
test (1.22.x, _test.gnolang.native)	34s
test (1.22.x, _test.gnolang.stdlibs)	59s
test (1.22.x, _test.gnolang.realm)	45s
test (1.22.x, _test.gnolang.pkg0)	2m 1s
test (1.22.x, _test.gnolang.pkg1)	6m 31s
test (1.22.x, _test.gnolang.pkg2)	4m 13s
test (1.22.x, _test.gnolang.other)	42s
upload-coverage	8s
	38m 34s

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