feat: Add `next_state` builtin change. #51

Job	Run time
ash-ci / mix deps.get	27s
ash-ci / mix hex.audit	17s
ash-ci / MIX_ENV=dev mix.compile	1m 50s
ash-ci / MIX_ENV=test mix.compile	2m 0s
ash-ci / mix credo --strict	44s
ash-ci / mix dialyzer	4m 51s
ash-ci / mix sobelow	32s
ash-ci / mix format --check-formatted	36s
ash-ci / mix spark.formatter --check	42s
ash-ci / mix test	1m 9s
ash-ci / mix deps.unlock --check-unused	31s
ash-ci / Release	0s
	13m 39s

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