docs: Random network example

[swo]

Minimal example of a randomly-generated network. Shows how to use an external graph-generating package to build connection networks.

Some open questions I think this PR poses:

1. Does this example belong here? How many examples do we want in this repo? One solution I could see, is having ~3 very well-curated examples here in this repo, and then another, more free-for-all ixa-examples repo.
2. Do we want to allow users to access rngs defined by define_rng!?. Right now, get_rng() is private, so users can't directly access the defined rngs or their states. In this example, I need to call an external-to-ixa function to generate the graph, and I might have wanted to use the rng state to seed the generation of that graph, rather than passing around a seed as if it were a separate parameter.

[github-actions]

Benchmark Results

Hyperfine

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
large_sir::baseline	3.6 ± 0.2	3.4	4.1	1.04 ± 0.06
large_sir::baseline_households	3.5 ± 0.1	3.4	4.1	1.00
large_sir::entities	7.8 ± 0.5	7.4	9.6	2.24 ± 0.17
large_sir::households	7.4 ± 0.4	7.2	10.0	2.14 ± 0.13

Criterion

Regressions (slower)

Group	Bench	Param	Change	CI Lower	CI Upper
large_dataset	bench_match_entity		33.446%	32.666%	34.208%
sample_entity	sample_entity_multi_property_indexed	10000	6.139%	5.579%	6.713%
sample_entity	sample_entity_multi_property_indexed	1000	5.729%	5.109%	6.335%
sample_entity	sample_entity_multi_property_indexed	100000	5.119%	3.770%	6.179%
sampling	count_and_sampling_single_known_length_entities		4.916%	4.571%	5.266%
examples	example-births-deaths		3.016%	2.758%	3.272%
sampling	sampling_single_l_reservoir_entities		1.954%	1.099%	2.683%
counts	index_after_adding_entities		1.464%	1.278%	1.649%
sampling	sampling_multiple_l_reservoir_entities		1.411%	1.030%	1.773%

Improvements (faster)

Group	Bench	Param	Change	CI Lower	CI Upper
large_dataset	bench_query_population_multi_indexed_entities		-29.488%	-30.194%	-28.738%
sample_entity	sample_entity_single_property_unindexed	10000	-20.833%	-23.217%	-18.348%
sample_entity	sample_entity_single_property_indexed	100000	-13.620%	-14.193%	-13.004%
sample_entity	sample_entity_single_property_indexed	10000	-13.018%	-13.697%	-12.218%
sample_entity	sample_entity_single_property_unindexed	1000	-8.331%	-9.528%	-7.182%
indexing	query_people_indexed_multi-property_entities		-6.167%	-6.537%	-5.866%
large_dataset	bench_filter_indexed_entity		-5.751%	-7.781%	-3.665%
examples	example-basic-infection		-3.401%	-3.769%	-3.068%
large_dataset	bench_query_population_indexed_property_entities		-3.001%	-4.860%	-1.136%
counts	multi_property_indexed_entities		-2.186%	-2.901%	-1.434%
indexing	with_query_results_multiple_individually_indexed_properties_enti		-2.098%	-2.852%	-1.524%

Unchanged / inconclusive (CI crosses 0%)

Group	Bench	Param	Change	CI Lower	CI Upper
large_dataset	bench_query_population_property_entities		1.743%	0.416%	3.461%
sample_entity	sample_entity_whole_population	10000	-1.494%	-3.165%	-0.192%
sampling	sampling_multiple_known_length_entities		1.034%	0.735%	1.347%
large_dataset	bench_query_population_derived_property_entities		0.949%	0.351%	1.514%
sampling	sampling_single_known_length_entities		-0.938%	-1.550%	-0.401%
large_dataset	bench_query_population_multi_unindexed_entities		-0.895%	-1.235%	-0.387%
large_dataset	bench_filter_unindexed_entity		0.888%	-2.405%	4.177%
indexing	with_query_results_indexed_multi-property_entities		-0.811%	-1.506%	-0.081%
counts	multi_property_unindexed_entities		-0.691%	-1.228%	-0.253%
sample_entity	sample_entity_whole_population	100000	-0.645%	-1.530%	0.081%
indexing	query_people_count_indexed_multi-property_entities		0.630%	0.206%	1.055%
counts	reindex_after_adding_more_entities		0.502%	0.360%	0.626%
indexing	query_people_count_single_indexed_property_entities		0.411%	-0.211%	0.959%
sampling	count_and_sampling_single_unindexed_concrete_plus_derived_entiti		-0.383%	-0.531%	-0.230%
indexing	query_people_count_multiple_individually_indexed_properties_enti		0.358%	0.232%	0.489%
sampling	sampling_single_unindexed_concrete_plus_derived_entities		-0.355%	-0.803%	0.077%
algorithm_benches	algorithm_sampling_single_l_reservoir		-0.314%	-0.715%	0.175%
algorithm_benches	algorithm_sampling_single_known_length		0.312%	-3.417%	4.348%
sampling	sampling_multiple_unindexed_entities		0.246%	0.131%	0.323%
counts	single_property_indexed_entities		0.194%	-0.433%	0.783%
indexing	query_people_multiple_individually_indexed_properties_entities		-0.185%	-0.638%	0.085%
indexing	query_people_single_indexed_property_entities		0.149%	-0.002%	0.295%
algorithm_benches	algorithm_sampling_multiple_l_reservoir		0.124%	-0.353%	0.757%
algorithm_benches	algorithm_sampling_single_rand_reservoir		0.066%	-0.202%	0.323%
indexing	with_query_results_single_indexed_property_entities		0.059%	-0.271%	0.361%
algorithm_benches	algorithm_sampling_multiple_known_length		0.059%	-0.325%	0.481%
sample_entity	sample_entity_single_property_unindexed	100000	0.057%	-0.420%	0.541%
counts	concrete_plus_derived_unindexed_entities		0.038%	-0.260%	0.311%
sample_entity	sample_entity_whole_population	1000	0.038%	-1.268%	1.199%
sampling	sampling_single_unindexed_entities		0.016%	-0.151%	0.146%
sample_entity	sample_entity_single_property_indexed	1000	-0.012%	-2.407%	2.318%
counts	single_property_unindexed_entities		0.001%	-0.526%	0.522%

Not Compared (no baseline yet)

Group	Bench	Reason
(none)