LazilyUnpickling{Dict,List}: add repr #3014

Job	Run time
Conda Pytest (ubuntu-latest)	4m 59s
Pylint	2m 26s
Flake8	20s
Conda Pytest (macos-latest)	12m 28s
Mypy	2m 7s
Tests for downstream project Firedrake	16m 45s
Conda Examples	2m 43s
Tests for downstream project arraycontext	3m 24s
Conda Pytest with Intel CL	4m 32s
Tests for downstream project meshmode	14m 54s
Conda Pytest without arg check	4m 52s
Documentation	2m 13s
Tests for downstream project grudge	8m 58s
Conda Pytest Twice (for cache behavior)	6m 20s
Tests for downstream project pytential	45m 59s
Tests for downstream project pytato	5m 45s
	2h 18m 45s

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