replace pyrsistent.PMap, immutables.Map with immutabledict #3327

Job	Run time
Documentation	1m 36s
Conda Examples	1m 53s
Tests for downstream project Firedrake	18m 11s
Tests for downstream project arraycontext	2m 28s
Tests for downstream project meshmode	44m 53s
Tests for downstream project grudge	11m 22s
Mypy	1m 32s
Tests for downstream project pytential	54m 43s
Pylint	1m 46s
Tests for downstream project pytato	6m 27s
Conda Pytest (ubuntu-latest)	3m 57s
Conda Pytest with Intel CL	4m 7s
Conda Pytest (macos-latest)	3m 57s
Conda Pytest without arg check	4m 2s
Conda Pytest Twice (for cache behavior)	5m 34s
Ruff	7s
Typos	8s
Validate CITATION.cff	7s
	2h 46m 50s

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