improvement: implement a subscription notification batcher #1189

Job	Run time
ash-ci / mix deps.get	15s
ash-ci / MIX_ENV=dev mix.compile	27s
ash-ci / audit	39s
ash-ci / MIX_ENV=test mix.compile	49s
ash-ci / mix docs	24s
ash-ci / Deploy docs to GitHub pages.	0s
ash-ci / mix format --check-formatted	49s
ash-ci / mix spark.cheat_sheets --check	38s
ash-ci / mix spark.formatter --check	34s
ash-ci / mix sobelow	43s
ash-ci / mix credo --strict	38s
ash-ci / mix dialyzer	3m 34s
ash-ci / mix test	1m 12s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix deps.unlock --check-unused	33s
ash-ci / Release	0s
	11m 15s

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