feat: implement `gno mod tidy` #1896

Job	Run time
build (1.20.x, GOARCH=amd64 GOOS=linux, gno)	16s
test (1.20.x, _test.cmd)	44s
build (1.20.x, GOARCH=wasm GOOS=js, gno)	41s
test (1.20.x, _test.pkg)	40s
build (1.21.x, GOARCH=amd64 GOOS=linux, gno)	43s
test (1.20.x, _test.gnolang.native)	20s
build (1.21.x, GOARCH=wasm GOOS=js, gno)	20s
test (1.20.x, _test.gnolang.stdlibs)	50s
test (1.20.x, _test.gnolang.realm)	42s
test (1.20.x, _test.gnolang.pkg0)	1m 46s
test (1.20.x, _test.gnolang.pkg1)	9m 19s
test (1.20.x, _test.gnolang.pkg2)	5m 4s
test (1.20.x, _test.gnolang.other)	18s
test (1.21.x, _test.cmd)	1m 20s
test (1.21.x, _test.pkg)	1m 12s
test (1.21.x, _test.gnolang.native)	1m 14s
test (1.21.x, _test.gnolang.stdlibs)	1m 50s
test (1.21.x, _test.gnolang.realm)	1m 13s
test (1.21.x, _test.gnolang.pkg0)	2m 36s
test (1.21.x, _test.gnolang.pkg1)	9m 58s
test (1.21.x, _test.gnolang.pkg2)	7m 18s
test (1.21.x, _test.gnolang.other)	1m 27s
upload-coverage	13s
	50m 4s

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