FlattenMapper: claim everything is an integer #3284

Job	Run time
Pylint	1m 40s
Mypy	1m 30s
Ruff	6s
Typos	3s
Documentation	1m 41s
Conda Examples	2m 1s
Conda Pytest (ubuntu-latest)	3m 54s
Conda Pytest with Intel CL	4m 3s
Conda Pytest (macos-latest)	3m 34s
Conda Pytest without arg check	3m 53s
Conda Pytest Twice (for cache behavior)	5m 16s
Tests for downstream project Firedrake	2m 1s
Validate CITATION.cff	8s
Tests for downstream project arraycontext	2m 40s
Tests for downstream project meshmode	10m 9s
Tests for downstream project grudge	10m 34s
Tests for downstream project pytential	54m 49s
Tests for downstream project pytato	6m 13s
	1h 54m 15s

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