LazilyUnpickling{Dict,List}: add repr #3055

Job	Run time
Flake8	24s
Conda Pytest (ubuntu-latest)	4m 7s
Conda Pytest (macos-latest)	10m 4s
Mypy	1m 49s
Pylint	2m 16s
Conda Pytest with Intel CL	4m 1s
Conda Pytest without arg check	4m 14s
Conda Pytest Twice (for cache behavior)	5m 21s
Documentation	2m 0s
Tests for downstream project Firedrake	15m 57s
Tests for downstream project arraycontext	2m 40s
Conda Examples	2m 14s
Tests for downstream project meshmode	11m 11s
Tests for downstream project grudge	7m 4s
Tests for downstream project pytential	33m 36s
Tests for downstream project pytato	5m 18s
	1h 52m 16s

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