Perf improvement: json_middleware

[pr-benchmarks]

Scenario	Environment	Date	Old RPS	New RPS	Change	Deviation	StDev	Dependencies
json_middleware [Fixed]	Json 400k 6- Trends Intel Win	08/08/2025 02:26:07	10,538	10,644	1.01 % (106) 👍	2.03 σ	52.45	Changes Name Version Diff Microsoft.AspNetCore.Antiforgery.dll 10.0.0-rc.1.25405.108 -> 10.0.0-rc.1.25406.102 dotnet/dotnet@a7417d8...30bc8f9 Microsoft.AspNetCore.App 10.0.0-rc.1.25405.108 -> 10.0.0-rc.1.25406.102 a7417d8...30bc8f9 Microsoft.NETCore.App 10.0.0-rc.1.25405.108 -> 10.0.0-rc.1.25406.102 dotnet/runtime@a7417d8...30bc8f9

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