chore: add clone support for entityset

[cdc-as81]

Summary

This PR makes EntitySet<'a, E> cloneable by deep-cloning its lazy expression tree and adding clone support for property-backed source leaves.

Changes

• implement Clone for EntitySet and EntitySetInner
• add clone_box() to AbstractPropertySource for cloning boxed property sources
• implement Clone for ConcretePropertySource and DerivedPropertySource
• implement Clone for SourceSet, including PropertySet
• add tests covering:
  • cloned composite set expressions
  • cloned unindexed concrete-property queries
  • cloned unindexed derived-property queries
  • clone independence when one copy is consumed

[github-actions]

Benchmark Results

Hyperfine

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
large_sir::baseline	2.8 ± 0.1	2.7	3.0	1.00
large_sir::entities	12.6 ± 0.1	12.4	12.8	4.44 ± 0.10

Criterion

Regressions (slower)

Group	Bench	Param	Change	CI Lower	CI Upper
sample_entity	sample_entity_single_property_unindexed	1000	20.133%	18.208%	22.081%
large_dataset	bench_match_entity		12.068%	11.628%	12.602%
large_dataset	bench_query_population_derived_property_entities		9.566%	8.279%	10.853%
sampling	sampling_single_unindexed_entities		3.738%	3.289%	4.165%
sampling	sampling_multiple_l_reservoir_entities		3.347%	2.945%	3.634%
sample_entity	sample_entity_single_property_unindexed	10000	3.206%	2.510%	4.158%
examples	example-basic-infection		3.101%	2.190%	3.930%
sampling	sampling_multiple_unindexed_entities		2.817%	2.410%	3.221%
algorithm_benches	algorithm_sampling_multiple_known_length		2.709%	2.443%	2.933%
examples	example-births-deaths		2.310%	1.918%	2.724%

Improvements (faster)

Group	Bench	Param	Change	CI Lower	CI Upper
indexing	query_people_single_indexed_property_entities		-15.238%	-16.065%	-14.462%
indexing	query_people_indexed_multi-property_entities		-9.258%	-9.867%	-8.714%
sampling	sampling_single_unindexed_concrete_plus_derived_entities		-6.377%	-6.745%	-5.992%
sample_entity	sample_entity_single_property_indexed	1000	-4.892%	-5.441%	-4.443%
sample_entity	sample_entity_single_property_indexed	10000	-4.365%	-4.748%	-4.067%
indexing	query_people_count_multiple_individually_indexed_properties_enti		-4.344%	-4.540%	-4.153%
sample_entity	sample_entity_multi_property_indexed	1000	-4.266%	-4.534%	-4.036%
sample_entity	sample_entity_multi_property_indexed	100000	-4.038%	-4.596%	-3.503%
indexing	with_query_results_indexed_multi-property_entities		-4.012%	-4.608%	-3.360%
counts	multi_property_indexed_entities		-3.625%	-4.136%	-3.154%
sample_entity	sample_entity_single_property_indexed	100000	-3.256%	-3.819%	-2.883%
sample_entity	sample_entity_multi_property_indexed	10000	-3.140%	-3.430%	-2.886%
sampling	count_and_sampling_single_unindexed_concrete_plus_derived_entiti		-2.166%	-2.342%	-1.975%
sampling	count_and_sampling_single_known_length_entities		-1.982%	-2.491%	-1.645%
sample_entity	sample_entity_single_property_unindexed	100000	-1.876%	-2.264%	-1.481%
large_dataset	bench_query_population_multi_unindexed_entities		-1.464%	-1.733%	-1.210%

Unchanged / inconclusive (CI crosses 0%)

Group	Bench	Param	Change	CI Lower	CI Upper
indexing	query_people_multiple_individually_indexed_properties_entities		1.443%	0.648%	2.004%
large_dataset	bench_filter_indexed_entity		1.243%	-6.556%	9.111%
large_dataset	bench_filter_unindexed_entity		1.175%	-1.950%	4.409%
large_dataset	bench_query_population_multi_indexed_entities		1.138%	0.778%	1.528%
sample_entity	sample_entity_whole_population	10000	1.067%	-0.189%	3.675%
indexing	query_people_count_indexed_multi-property_entities		1.037%	0.823%	1.283%
sampling	sampling_single_known_length_entities		-1.006%	-1.360%	-0.614%
indexing	query_people_count_single_indexed_property_entities		-0.782%	-1.067%	-0.514%
counts	index_after_adding_entities		-0.585%	-0.741%	-0.439%
algorithm_benches	algorithm_sampling_single_known_length		-0.584%	-1.093%	-0.154%
algorithm_benches	algorithm_sampling_multiple_l_reservoir		0.562%	0.135%	1.032%
sampling	sampling_single_l_reservoir_entities		-0.428%	-0.497%	-0.355%
indexing	with_query_results_single_indexed_property_entities		0.383%	-0.164%	1.002%
algorithm_benches	algorithm_sampling_single_l_reservoir		-0.361%	-0.937%	0.050%
large_dataset	bench_query_population_indexed_property_entities		0.299%	0.042%	0.560%
counts	single_property_indexed_entities		-0.287%	-0.658%	0.014%
sampling	sampling_multiple_known_length_entities		0.262%	-0.002%	0.536%
counts	reindex_after_adding_more_entities		-0.256%	-0.452%	-0.046%
sample_entity	sample_entity_whole_population	1000	-0.243%	-0.655%	0.291%
indexing	with_query_results_multiple_individually_indexed_properties_enti		0.205%	-0.608%	0.884%
counts	single_property_unindexed_entities		-0.187%	-0.984%	0.488%
sample_entity	sample_entity_whole_population	100000	-0.174%	-0.493%	0.280%
counts	multi_property_unindexed_entities		-0.164%	-1.317%	0.791%
large_dataset	bench_query_population_property_entities		-0.154%	-0.741%	0.312%
counts	concrete_plus_derived_unindexed_entities		0.090%	-0.506%	0.820%
algorithm_benches	algorithm_sampling_single_rand_reservoir		0.050%	-0.169%	0.335%