feat: implement StreamCreateForecasts

[devsjc]

Adds a new RPC, StreamCreateForecasts, that enables the quick creation of multiple forecasts at one time. These forecasts are all created in one atomic block, so if something goes wrong with any of them, none of them are entered into the database. This route and behaviour is a result of conversation with @dfulu.

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• 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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[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":"2026-07-15T10:21:31Z","message":"Completed migrations"}
goos: linux
goarch: amd64
pkg: github.com/openclimatefix/data-platform/internal/server/postgres
cpu: AMD EPYC 9V74 80-Core Processor                
BenchmarkPostgresClient/small/GetForecastAsTimeseries-4         	      51	  22161402 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	     192	   6118523 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	     980	   1138055 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	     129	   8954766 ns/op
BenchmarkPostgresClient/small/StreamForecastData-4              	      20	  54346252 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	59.697s
?   	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         24.16m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4          6.560m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4     1.274m ± ∞ ¹
PostgresClient/small/CreateForecast-4                  11.24m ± ∞ ¹
PostgresClient/small/StreamForecastData-4              53.98m ± ∞ ¹
geomean                                                10.41m
¹ need >= 6 samples for confidence interval at level 0.95

cpu: AMD EPYC 9V74 80-Core Processor                
                                                   │ bench-devsjc-streamcreateforecasts.txt │
                                                   │                 sec/op                 │
PostgresClient/small/GetForecastAsTimeseries-4                                 22.16m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4                                  6.119m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4                             1.138m ± ∞ ¹
PostgresClient/small/CreateForecast-4                                          8.955m ± ∞ ¹
PostgresClient/small/StreamForecastData-4                                      54.35m ± ∞ ¹
geomean                                                                        9.443m
¹ need >= 6 samples for confidence interval at level 0.95