feat: add scope merging mechanism

[giortzisg]

Description

Issues

• resolves: Add scope merging for global and isolation scopes #1369
• resolves: GO-155

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Reminders

• Add GH Issue ID & Linear ID
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
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[linear-code]

GO-155

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[sentry]

Bug: Manually set trace contexts on the scope are now silently ignored for error events due to an unconditional skip. This breaks error-to-trace linking for users relying on this feature.
_{Severity: MEDIUM}

Suggested Fix

Restore the previous conditional logic in the loop within mergeScope. The check for the trace key should only continue if the event is a transaction. Re-add the && event.Type == transactionType condition to the if statement to allow error events to correctly inherit the trace context from the scope.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: scope.go#L430-L432

Potential issue: The refactoring in `mergeScope` unconditionally skips the `trace`
context from the scope. Previously, this context was only skipped for transaction
events, allowing error events to use a manually set trace context. This was documented
behavior used "to link errors and traces/spans in Sentry." The new implementation
silently ignores any manually set `trace` context on the scope for error events,
breaking this functionality. The automatic trace resolution via `applyTraceToEvent` does
not provide an alternative for this manual use case, resulting in a regression where
error events may no longer be correctly linked to traces if a user was relying on this
manual mechanism.