Add mobile normalizations to SpanV2 processing pipeline

[buenaflor]

The V2 span processing pipeline has no mobile-specific normalizations. All mobile logic lives in the V1 path (Event + Span types).

Mobile specific normalization for span v2

• Outlier filtering: Remove app.start.cold.value, app.start.warm.value, app.ttid.value, app.ttfd.value exceeding 180s
• Main thread tag: Derive sentry.main_thread: "true" from thread.name == "main"
• Device class: Derive device.class (LOW/MEDIUM/HIGH) from device attributes. Reuse existing classification logic from device_class.rs
• Mobile tag: Derive sentry.mobile: "true" from sentry.sdk.name

Frame rate calculation: Derive frames.frozen_rate and frames.slow_rate from frames.frozen / frames.total and frames.slow / frames.total and stall_percentage -> done in Frontend instead on-demand

[linear-code]

RELAY-210

[buenaflor]

note that maybe it also makes sense to move some of them to frontend queries