Migrate HTTP resilience integration from deprecated `Microsoft.Extensions.Http.Polly`

**Description**

`Microsoft.Extensions.Http.Polly` is deprecated in favor of `Microsoft.Extensions.Http.Resilience`. Replace the deprecated integration while preserving the SDK’s existing retry and resilience behavior across supported target frameworks.

**Scope**

- Replace `Microsoft.Extensions.Http.Polly` with `Microsoft.Extensions.Http.Resilience`.
- Update HTTP client resilience configuration to the new APIs.
- Preserve existing retry timing, retry count, and handled failure conditions.
- Update unit tests and package lock files.
- Remove the deprecated package after all usages are migrated.
- Confirm compatibility with `netstandard2.0`, `netstandard2.1`, `net462`, and the current modern .NET target.
- Exclude Broker API functionality.

**Acceptance criteria**

- No project references `Microsoft.Extensions.Http.Polly`.
- Existing resilience behavior remains covered by tests.
- Restore, Debug tests, Release build, and package validation pass without warnings.
- Lock files are regenerated and committed.
- Public API compatibility remains unchanged, or intentional differences are documented.
- Documentation and examples referencing the old integration are updated.

**References**

- [Microsoft.Extensions.Http.Polly deprecation notice](https://www.nuget.org/packages/Microsoft.Extensions.Http.Polly)
- [Microsoft.Extensions.Http.Resilience](https://www.nuget.org/packages/Microsoft.Extensions.Http.Resilience)