Apply scope attributes to Rust logs and metrics with spec precedence rules

Once first-class scope attributes exist in `sentry-core`[ (see ]()[RUST-183](https://linear.app/getsentry/issue/RUST-183/add-first-class-scope-attributes-apis-to-sentry-core)), Rust should apply them to emitted logs and metrics at capture time. The [Attributes spec]() says attributes from the scope chain are applied when telemetry is captured, that global and isolation scope attributes **MUST** apply to logs and metrics, and that telemetry-item attributes (`log` / `metric`) **MUST** take precedence over scope attributes.

This issue should implement scope-attribute merging in the Rust log and metric capture pipelines, preserving explicitly set log/metric attributes. Relevant code paths today are `sentry-core/src/client.rs`, `sentry-core/src/scope/real.rs`, and the existing log/metric tests in `sentry-core/tests/metrics.rs`. If desired, span handling can be evaluated separately, but logs and metrics are already explicitly covered by the spec text.