replace pyrsistent.PMap, immutables.Map with immutabledict #3370

Job	Run time
Mypy	1m 28s
Ruff	10s
Documentation	1m 31s
Tests for downstream project Firedrake	2m 38s
Tests for downstream project arraycontext	2m 27s
Conda Examples	1m 56s
Tests for downstream project meshmode	6m 56s
Tests for downstream project grudge	6m 57s
Pylint	1m 22s
Conda Pytest (ubuntu-latest)	4m 5s
Conda Pytest with Intel CL	3m 45s
Tests for downstream project pytential	6m 57s
Conda Pytest (macos-latest)	3m 20s
Tests for downstream project pytato	6m 36s
Conda Pytest without arg check	3m 55s
Conda Pytest Twice (for cache behavior)	5m 16s
Typos	6s
Validate CITATION.cff	7s
	59m 32s

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