Link structured logs with captured session replays

[tustanivsky]

This PR adds automatic linking between structured logs and captured session replays on platforms where the plugin provides its own replay recording - desktop (sentry-native) and Apple (sentry-cocoa).

When session replay capturing is enabled and the recorder initializes successfully, the SDK now sets two scope-level log attributes (in addition to the existing contexts.replay.replay_id used for events):

• sentry.replay_id - the session's replay id, allowing Sentry to associate logs with the corresponding replay
• sentry._internal.replay_is_buffering: true - marks the replay link as provisional, since the Unreal SDK records replays into a local rolling video file and uploads them only when a crash occurs (equivalent to the buffer/onError mode in other SDKs)

Both attributes are set once during SDK initialization via the existing SetAttribute wrapper (sentry_set_attribute on native, Scope.setAttributeValue on cocoa). The underlying SDKs automatically apply scope attributes to every log at capture time, so there is no per-log overhead. This works for all log sources: the Log* subsystem API, Blueprint calls, and the automatic UE log forwarding.

Example replay with linked logs.

Related items:

• Add integration with Session Replay product for native platforms #1445
• Add integration with Session Replay product for Apple platforms #1468