Unbounded in-memory data growth causes OOM on long-running servers

[Manik-Khajuria-5]

Bug Description

Several server-side data structures in visdom grow without bounds during normal usage.
On long-running servers, memory usage continuously increases until the process is eventually terminated by the OS due to Out-Of-Memory (OOM).

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Reproduction Steps

Run a long training session with frequent images/logs/embedding updates.
RAM usage continuously increases until the server is killed.

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Expected behavior
Memory usage should remain bounded.

Suggested Fix
Add caps/history limits and use bounded queues (deque(maxlen=N)).