Add pgrouting tests

nix/tests/expected/pgrouting.out

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+create schema v;
+-- create the roads table
+create table v.roads (
+  id serial primary key,
+  source integer,
+  target integer,
+  cost double precision
+);
+-- insert sample data into roads table
+insert into v.roads (source, target, cost) values
+(1, 2, 1.0),
+(2, 3, 1.0),
+(3, 4, 1.0),
+(1, 3, 2.5),
+(3, 5, 2.0);
+-- create a function to use pgRouting to find the shortest path
+select * from pgr_dijkstra(
+  'select id, source, target, cost from v.roads',
+  1, -- start node
+  4  -- end node
+);
+ seq | path_seq | node | edge | cost | agg_cost 
+-----+----------+------+------+------+----------
+   1 |        1 |    1 |    1 |    1 |        0
+   2 |        2 |    2 |    2 |    1 |        1
+   3 |        3 |    3 |    3 |    1 |        2
+   4 |        4 |    4 |   -1 |    0 |        3
+(4 rows)
+
+drop schema v cascade;
+NOTICE:  drop cascades to table v.roads

nix/tests/sql/pgrouting.sql

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+create schema v;
+
+-- create the roads table
+create table v.roads (
+  id serial primary key,
+  source integer,
+  target integer,
+  cost double precision
+);
+
+-- insert sample data into roads table
+insert into v.roads (source, target, cost) values
+(1, 2, 1.0),
+(2, 3, 1.0),
+(3, 4, 1.0),
+(1, 3, 2.5),
+(3, 5, 2.0);
+
+-- create a function to use pgRouting to find the shortest path
+select * from pgr_dijkstra(
+  'select id, source, target, cost from v.roads',
+  1, -- start node
+  4  -- end node
+);
+
+drop schema v cascade;
+