feat: Safer storage optimization

[devsjc]

Some changes that had been made in the dev database meant the migration did not work. I'm confident it would have been fine in prod, but in order to get it deployed in dev, it needs to be a more defensive migration.

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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[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":"2026-06-17T22:50:10Z","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         	      45	  24507414 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	     186	   6337952 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	     890	   1279611 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	     106	  10865809 ns/op
BenchmarkPostgresClient/small/StreamForecastData-4              	      22	  50672847 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	67.194s
?   	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-surer-optimization-migration.txt │
                                                   │     sec/op     │        sec/op          vs base                │
PostgresClient/small/GetForecastAsTimeseries-4         22.24m ± ∞ ¹            24.51m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetForecastAtTimestamp-4          6.149m ± ∞ ¹            6.338m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetObservationsAsTimeseries-4     1.256m ± ∞ ¹            1.280m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/CreateForecast-4                  10.79m ± ∞ ¹            10.87m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/StreamForecastData-4              51.18m ± ∞ ¹            50.67m ± ∞ ¹       ~ (p=1.000 n=1) ²
geomean                                                9.894m                  10.18m        +2.91%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05