resolves #10931

1. Replaced Newtonsoft.Json with System.Text.Json for deserializing worker profiles.
2. Previously, all worker configs were loaded and parsed into RpcWorkerDescription objects before filtering using ShouldAddWorkerConfig. Now, we skip loading configs for non-matching runtimes and only parse the config that matches FUNCTIONS_WORKER_RUNTIME, reducing unnecessary overhead after specialization.

This change reduced allocations in the AddProviders method, during specialization (and even during placeholder mode).

Before

After

Delta

• RpcWorkerConfigFactory.AddProviders() - Total allocations dropped by 1,518 (30.13%).
• RpcWorkerConfigFactory.AddProviders() - Total allocated size reduced by ~238 KB (nearly 50%).

Before

After

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

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Additional PR information