feat(r/staker): Add referral support to Staker `StakeToken` function #124

Job	Run time
test-gnoswap (p/uint256, gno/examples/gno.land/p/gnoswap/uint256)	26s
test-gnoswap (p/int256, gno/examples/gno.land/p/gnoswap/int256)	20s
test-gnoswap (p/gnsmath, gno/examples/gno.land/p/gnoswap/gnsmath)	21s
test-gnoswap (r/common, gno/examples/gno.land/r/gnoswap/v1/common)	26s
test-gnoswap (r/gns, gno/examples/gno.land/r/gnoswap/v1/gns)	33s
test-gnoswap (r/gnft, gno/examples/gno.land/r/gnoswap/v1/gnft)	31s
test-gnoswap (r/gov/xgns, gno/examples/gno.land/r/gnoswap/v1/gov/xgns)	31s
test-gnoswap (r/emission, gno/examples/gno.land/r/gnoswap/v1/emission)	23s
test-gnoswap (r/protocol_fee, gno/examples/gno.land/r/gnoswap/v1/protocol_fee)	18s
test-gnoswap (r/pool, gno/examples/gno.land/r/gnoswap/v1/pool)	3m 34s
test-gnoswap (r/position, gno/examples/gno.land/r/gnoswap/v1/position)	1m 40s
test-gnoswap (r/router, gno/examples/gno.land/r/gnoswap/v1/router)	1m 36s
test-gnoswap (r/staker, gno/examples/gno.land/r/gnoswap/v1/staker)	3m 24s
test-gnoswap (r/community_pool, gno/examples/gno.land/r/gnoswap/v1/community_pool)	19s
test-gnoswap (r/gov/staker, gno/examples/gno.land/r/gnoswap/v1/gov/staker)	37s
test-gnoswap (r/gov/governance, gno/examples/gno.land/r/gnoswap/v1/gov/governance)	1m 1s
test-gnoswap (r/launchpad, gno/examples/gno.land/r/gnoswap/v1/launchpad)	1m 12s
	17m 12s

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