feat(dataserver): Forecast target period tracking; simplifications

[devsjc]

• Have you followed the Open Climate Fix Contribution Guidelines?
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• Have you successfully run make test with your changes locally?

Fixes a bug whereby null metadata was not being correctly handled in the CreateForecast route.
Also

• Renames the locations table for greater understandability.
• Adds a target_period to each forecast object to track the forecast range
• Simplifies GetForecastAtTimestamp query and route logic
• Adds DeleteForeacst RPC

Closes #25

[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":"2025-11-07T09:57:48Z","message":"Running migrations"}
goos: linux
goarch: amd64
pkg: github.com/openclimatefix/data-platform/internal/server/postgres
cpu: AMD EPYC 7763 64-Core Processor                
BenchmarkPostgresClient/6144000/GetForecastAsTimeseries-4         	     181	   6412454 ns/op
BenchmarkPostgresClient/6144000/GetForecastAtTimestamp-4          	      38	  29859384 ns/op
BenchmarkPostgresClient/6144000/GetObservationsAsTimeseries-4     	     880	   1279604 ns/op
BenchmarkPostgresClient/6144000/CreateForecast-4                  	     309	   3457436 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	114.622s
?   	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-location-table-rename.txt │
                                                     │     sec/op     │    sec/op      vs base                 │
PostgresClient/6144000/GetForecastAsTimeseries-4         4.826m ± ∞ ¹    6.412m ± ∞ ¹        ~ (p=1.000 n=1) ²
PostgresClient/6144000/GetForecastAtTimestamp-4         105.00m ± ∞ ¹    29.86m ± ∞ ¹        ~ (p=1.000 n=1) ²
PostgresClient/6144000/GetObservationsAsTimeseries-4     1.307m ± ∞ ¹    1.280m ± ∞ ¹        ~ (p=1.000 n=1) ²
PostgresClient/6144000/CreateForecast-4                  2.612m ± ∞ ¹    3.457m ± ∞ ¹        ~ (p=1.000 n=1) ²
geomean                                                  6.449m          5.395m        -16.35%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05

[devsjc]

Not sure why this has majorly sped up the benchmark for GetForecastAtTimestamp - going to investigate tomorrow.

[devsjc]

Modified the entire table and query structure to improve theGetForecastAtTimestamp query, and forecasts table at large; now the speedup is warranted!