feat(api): Speedier streaming of forecast data

[devsjc]

Contribution Checklist

• Have you followed the Open Climate Fix Contribution Guidelines?
• Have you referenced the Issue this PR addresses, where applicable?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added a summary of the changes?
• Have you written new tests for your changes, where applicable?
• Have you successfully run make lint with your changes locally?
• Have you successfully run make test with your changes locally?

Warning

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Changes in this Pull Request

Modifies the index on the sources materialized view, and updates the underlying sql of the StreamForecastData implementation. Also modifues the schema to take a list of location uuids, and uses the connection pool directly, to enable controllable parallelisation of the query in-api, as opposed to by-client.

[github-actions]

Benchmark Results

Benchmark results

?   	github.com/openclimatefix/data-platform/cmd	[no test files]
?   	github.com/openclimatefix/data-platform/internal/gen/ocf/dp	[no test files]
?   	github.com/openclimatefix/data-platform/internal/interceptors	[no test files]
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/dummy	0.005s
{"level":"debug","time":"2026-05-05T14:10:57Z","message":"Completed migrations"}
goos: linux
goarch: amd64
pkg: github.com/openclimatefix/data-platform/internal/server/postgres
cpu: AMD EPYC 7763 64-Core Processor                
BenchmarkPostgresClient/small/GetForecastAsTimeseries-4         	      68	  16130566 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	     274	   4220812 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	     903	   1262189 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	      88	  13040860 ns/op
BenchmarkPostgresClient/small/StreamForecastData-4              	      12	 112371981 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	71.592s
?   	github.com/openclimatefix/data-platform/internal/server/postgres/gen	[no test files]

Benchmark vs base branch

goos: linux
goarch: amd64
pkg: github.com/openclimatefix/data-platform/internal/server/postgres
cpu: AMD EPYC 7763 64-Core Processor                
                                                   │ bench-main.txt │  bench-devsjc-faster-streaming.txt   │
                                                   │     sec/op     │    sec/op     vs base                │
PostgresClient/small/GetForecastAsTimeseries-4         16.51m ± ∞ ¹   16.13m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetForecastAtTimestamp-4          4.200m ± ∞ ¹   4.221m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetObservationsAsTimeseries-4     1.273m ± ∞ ¹   1.262m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/CreateForecast-4                  13.00m ± ∞ ¹   13.04m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/StreamForecastData-4                             112.4m ± ∞ ¹
geomean                                                5.821m         10.47m        -0.60%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05