feat(proto): Add p2,98,25,75; refactor tests

[devsjc]

Adds 4 more p-levels to the predicted generation values table. These cost nothing storage-wise if they are unused. Also refactors the test suite a little bit.

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":"2026-07-07T10:34:13Z","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         	      45	  25021931 ns/op
BenchmarkPostgresClient/small/GetForecastAtTimestamp-4          	     178	   6543182 ns/op
BenchmarkPostgresClient/small/GetObservationsAsTimeseries-4     	     966	   1159993 ns/op
BenchmarkPostgresClient/small/CreateForecast-4                  	     124	   9282810 ns/op
BenchmarkPostgresClient/small/StreamForecastData-4              	      20	  55648845 ns/op
PASS
ok  	github.com/openclimatefix/data-platform/internal/server/postgres	60.554s
?   	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 9V74 80-Core Processor                
                                                   │ bench-main.txt │    bench-devsjc-more-plevels.txt     │
                                                   │     sec/op     │    sec/op     vs base                │
PostgresClient/small/GetForecastAsTimeseries-4         22.11m ± ∞ ¹   25.02m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetForecastAtTimestamp-4          5.758m ± ∞ ¹   6.543m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/GetObservationsAsTimeseries-4     1.154m ± ∞ ¹   1.160m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/CreateForecast-4                  9.036m ± ∞ ¹   9.283m ± ∞ ¹       ~ (p=1.000 n=1) ²
PostgresClient/small/StreamForecastData-4              52.85m ± ∞ ¹   55.65m ± ∞ ¹       ~ (p=1.000 n=1) ²
geomean                                                9.316m         9.962m        +6.93%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05