fix: properly avoid type casts on maps w/ fields #880

Job	Run time
ash-ci / Community Files Check	3s
ash-ci / audit	1m 24s
ash-ci / REUSE compliance	14s
ash-ci / mix igniter.upgrade	7s
ash-ci / MIX_ENV=test mix.compile	35s
ash-ci / Report Mix Dependencies	15s
ash-ci / mix dialyzer	3m 38s
ash-ci / mix spark.cheat_sheets --check	31s
ash-ci / mix spark.formatter --check	5s
ash-ci / MIX_ENV=dev mix.compile	33s
ash-ci / mix format --check-formatted	32s
ash-ci / mix test	1m 10s
ash-ci / mix credo --strict	1m 30s
ash-ci / mix sobelow	35s
ash-ci / mix git_ops.check_message	0s
ash-ci / mix doctor --full --raise	0s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix deps.unlock --check-unused	0s
ash-ci / mix docs	2m 8s
ash-ci / Deploy docs to GitHub pages.	9s
ash-ci / Release	0s
ash-ci / NIF ${{ matrix.nif }} - ${{ matrix.job.target }} (${{ matrix.job.os }})	0s
	13m 29s

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