HybridCache: add net10 HybridCache zero-alloc fetch API

[mgravell]

implements span/DISH API for HybridCache as proposed in #112866 and agreed at API review, 2025-04-08

Concrete implementation (i.e. an override) will be added over in dotnet/extensions

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[Copilot]

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/libraries/Microsoft.Extensions.Caching.Abstractions/ref/Microsoft.Extensions.Caching.Abstractions.csproj: Language not supported

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[mgravell]

@dotnet/area-extensions-caching any chance of eyeballs?

[adamsitnik]

LGTM, thank you for your contribution @mgravell !

[adamsitnik]

/ba-g The System.Net.Http.Functional.Test seems to be just a flaky networking test (0.5% failure rate)