feat!: add scope merging mechanism

[giortzisg]

Description

This adds the scope merging mechanism by allocating a captureState object and copying all needed event attributes in place. This removes taking multiple scope clones on every capture.

The PR also includes breaking changes around EventModifier. The EventModifier was an agnostic modifier that was passed on ApplyToEvent. This duplicated the EventProcessor behavior and also complicated the scope merging mechanism, since we need to have a concrete *Scope type to merge the scopes. Furthermore, there is no documented behavior or signature for any EventModifier and this seems to be just the first archaic way to modify events before EventProcessor and BeforeSend hooks where a thing. Thus decided to remove this and have a concrete *Scope passed on ApplyToEvent. This behavior aligns with other sdks that pass a concrete scope.

This affects the public API with all the CaptureX methods now requiring a concrete scope to be passed, but further scope changes in the stack also change the CaptureX APIs to work with context.Context, so this change seems acceptable. Functionality isn't really removed but just shifted to BeforeSend hooks as intended.

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:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[linear-code]

GO-155

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