fix(cmd/gno/clean): allow to run `gno clean -modcache` from anywhere + rename and use `gnomod.ModCachePath` + tmp `GNOHOME` in main tests #6006

Job	Run time
setup	5s
Run Main (gnodev) / Go Linter / lint	50s
Run Main (gnodev) / Go Build / generated	12s
Run Main (gnodev) / Go Test / test	58s
Run Main (gnofaucet) / Go Build / generated	10s
Run Main (gnofaucet) / Go Linter / lint	30s
Run Main (gnogenesis) / Go Build / generated	17s
Run Main (gnofaucet) / Go Test / test	38s
Run Main (gnogenesis) / Go Linter / lint	54s
Run Main (gnogenesis) / Go Test / test	43s
Run Main (gnokeykc) / Go Build / generated	14s
Run Main (gnokeykc) / Go Linter / lint	35s
Run Main (gnokeykc) / Go Test / test	36s
Run Main (gnomd) / Go Linter / lint	42s
Run Main (gnomd) / Go Build / generated	18s
Run Main (gnomd) / Go Test / test	1m 11s
Run Main (gnomigrate) / Go Build / generated	54s
Run Main (gnomigrate) / Go Linter / lint	55s
Run Main (gnomigrate) / Go Test / test	43s
	11m 25s

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