Flush log buffer in base Client.close() #19347

Problem

When client.close() is called, the log buffer is not flushed. The close() method in platform SDKs (node-core, deno) only removes the exit event listener but doesn't call _INTERNAL_flushLogsBuffer(this). This means pending logs can be lost if someone explicitly closes the client.

Proposed Solution

Add _INTERNAL_flushLogsBuffer(this) to the base Client.close() in packages/core/src/client.ts so all SDKs benefit automatically, rather than fixing it in each platform SDK individually.

References

• Discussion: feat(deno): Export logs API from Deno SDK #19313 (comment)
• Node-core client: packages/node-core/src/sdk/client.ts (same pattern)
• Deno client: packages/deno/src/client.ts (same pattern)