CometTaskMemoryManager logs a warning and a memory dump every time a native reservation is refused #6257

What is the problem the feature request solves?

Native operators ask for memory with try_grow until they are refused, and then they spill. A partial grant from Spark is the normal spill signal, not an error. But CometTaskMemoryManager.acquireMemory logs a warning and calls TaskMemoryManager.showMemoryUsage() every time Spark grants less than was asked (CometTaskMemoryManager.java#L74-L85), and showMemoryUsage() logs another line per consumer at INFO. In a four-task aggregate with 96 MB of off-heap memory, that was 257 warnings in about five seconds. A query that spills heavily keeps producing them for its whole run. That buries real warnings and makes a healthy spill look like a failure.

Describe the potential solution

Log the partial grant at DEBUG, or at most once per task at INFO. Nothing is lost when a reservation really does fail: the error the pool returns already says how much was granted and lists the top consumers.

Additional context

No response