fix(sql): Cleanup array migration

[devsjc]

Adds the final migration in to cleanup the array based storage move.

[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":"2026-08-13T10:42:11Z","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         	     142	   7881569 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	     328	   3509615 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	    1004	   1138001 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	     364	   3044997 ns/op
BenchmarkPostgresClient/small/StreamForecastData-4              	      28	  40619274 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	36.664s
?   	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         11.44m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4          4.230m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4     1.304m ± ∞ ¹
PostgresClient/small/CreateForecast-4                  13.72m ± ∞ ¹
PostgresClient/small/StreamForecastData-4              62.53m ± ∞ ¹
geomean                                                8.845m
¹ need >= 6 samples for confidence interval at level 0.95

cpu: AMD EPYC 9V74 80-Core Processor                
                                                   │ bench-devsjc-migration-cleanup.txt │
                                                   │               sec/op               │
PostgresClient/small/GetForecastAsTimeseries-4                             7.882m ± ∞ ¹
PostgresClient/small/GetForecastAtTimestamp-4                              3.510m ± ∞ ¹
PostgresClient/small/GetObservationsAsTimeseries-4                         1.138m ± ∞ ¹
PostgresClient/small/CreateForecast-4                                      3.045m ± ∞ ¹
PostgresClient/small/StreamForecastData-4                                  40.62m ± ∞ ¹
geomean                                                                    5.225m
¹ need >= 6 samples for confidence interval at level 0.95