Perf improvement: json_middleware

[pr-benchmarks]

Scenario	Environment	Date	Old RPS	New RPS	Change	Deviation	StDev	Dependencies
json_middleware [Fixed]	Json 400k 2- Trends Intel Linux	05/17/2025 22:01:16	11,768	11,788	0.17 % (20) 👍	2.69 σ	7.33	Changes Name Version Diff Microsoft.AspNetCore.Antiforgery.dll 10.0.0-preview.5.25263.108 -> 10.0.0-preview.5.25265.101 dotnet/dotnet@362a422...ad85650 Microsoft.AspNetCore.App 10.0.0-preview.5.25263.108 -> 10.0.0-preview.5.25265.101 362a422...ad85650 Microsoft.NETCore.App 10.0.0-preview.5.25263.108 -> 10.0.0-preview.5.25265.101 dotnet/runtime@362a422...ad85650

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