feat(core): Export BeforeFinishCallback type (#8999)

Author: krystofwoldrich

packages/core/src/tracing/index.ts

@@ -1,5 +1,6 @@
 export { startIdleTransaction, addTracingExtensions } from './hubextensions';
 export { IdleTransaction, TRACING_DEFAULTS } from './idletransaction';
+export type { BeforeFinishCallback } from './idletransaction';
 export { Span, spanStatusfromHttpCode } from './span';
 export { Transaction } from './transaction';
 export { extractTraceparentData, getActiveTransaction } from './utils';