📜 Description

This PR introduces SentryMetrics wrapper class that bridges the Swift-only metrics API (count, distribution, gauge) to Objective-C.

This pattern was used because there is no way to make the underlying types @objc-compatible:

• SentryUnit is a Swift enum with associated values
• SentryAttributeValue is a Swift protocol
• SentryMetricsApi is a generic struct which also cannot be `@objc

Even though the static type of SentrySDK.metrics changed from SentryMetricsApiProtocol to SentryMetrics, read access remains fully backward-compatible because SentryMetrics conforms to SentryMetricsApiProtocol, so existing Swift call sites and variables typed as the protocol continue to work.

The actual breaks would only be:

• Assigning a custom conformer to the property: SentrySDK.metrics = MyCustomImpl()
• Explicitly using the old concrete type: let m: SentryMetricsApi<...> = SentrySDK.metrics

However, neither of these look like supported use-cases.

💡 Motivation and Context

The Unreal Engine plugin uses sentry-cocoa internally via Objective-C which previously had no access to the metrics API. This change enables metrics calls from any Objective-C context by accepting String for units and [String: Any] for attributes converting them to the Swift-native types internally.

Related items:

• Sentry Metrics for Unreal SDK sentry-unreal#1213
• Add Metrics API support sentry-unreal#1214

💚 How did you test it?

Manually emitted counter, gauge, and distribution metrics in Unreal Engine using a patched version of the Cocoa SDK in the plugin.

📝 Checklist

You have to check all boxes before merging:

• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.