fix(queries): Look back 3 days from start for forecasts

[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?
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• Have you successfully run make test with your changes locally?

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Changes in this Pull Request

Modifies the lookback from start on timeseries forcast collection to 3 days instead of 2. This is because, whilst the forecast may be only 2 days long, we often floor to 6 hours for the start of the lookback.
Addresses openclimatefix/quartz-api#217

[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":"2026-03-23T10:33:12Z","message":"Completed migrations"}
goos: linux
goarch: amd64
pkg: github.com/openclimatefix/data-platform/internal/server/postgres
cpu: Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz
BenchmarkPostgresClient/small/GetForecastAsTimeseries-4         	      52	  21739040 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	      75	  15743107 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	    1062	   1062694 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	      81	  14143920 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	68.415s
?   	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 │
                                                   │     sec/op     │
PostgresClient/small/GetForecastAsTimeseries-4         21.65m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4          15.26m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4     1.291m ± ∞ ¹
PostgresClient/small/CreateForecast-4                  15.37m ± ∞ ¹
geomean                                                8.998m
¹ need >= 6 samples for confidence interval at level 0.95

cpu: Intel(R) Xeon(R) Platinum 8370C CPU @ 2.80GHz
                                                   │ bench-devsjc-yellow-line-fix.txt │
                                                   │              sec/op              │
PostgresClient/small/GetForecastAsTimeseries-4                           21.74m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4                            15.74m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4                       1.063m ± ∞ ¹
PostgresClient/small/CreateForecast-4                                    14.14m ± ∞ ¹
geomean                                                                  8.469m
¹ need >= 6 samples for confidence interval at level 0.95