refactor(http)!: nest standard hedge options

[thomhurst]

Summary

• reshape StandardHedgeShieldOptions into nested handler, routing, circuit-breaker, concurrency-limit, attempt-timeout, total-timeout, and hedge options
• bind nested configuration keys and reject obsolete flat aliases with migration guidance
• preserve callbacks, endpoint snapshots, defaults, public API docs, samples, and integration behavior

Motivation

Align the standard hedge API with StandardHttpShieldOptions so configuration and code use the same composable options model.

Closes #331

Validation

• dotnet build Kevlar.slnx -c Release
• dotnet run --project tests/Kevlar.Tests -c Release --no-build --framework net8.0 -- --timeout 5m (1208 passed)
• dotnet run --project tests/Kevlar.Tests -c Release --no-build --framework net10.0 -- --timeout 5m (1239 passed)
• dotnet run --project tests/Kevlar.IntegrationTests -c Release --no-build -- --timeout 5m (166 passed)
• API/docs/changelog verifiers, package creation, snippet compilation (implicit and explicit usings), and Docusaurus production build

[coderabbitai]

Important

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 1bf11b71-eb8a-40e7-bbff-1f627f8bf664

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