chore: increase nvl monitor validate freq (#527)

## Description
<!-- Describe what this PR does -->
Increase the frequency of the validate_and_sync_nmxm_info function,
which cleans up stale partitions and fixes other issues stemming from
NMX-M problems.

## Type of Change
<!-- Check one that best describes this PR -->
- [ ] **Add** - New feature or capability
- [ ] **Change** - Changes in existing functionality  
- [ ] **Fix** - Bug fixes
- [ ] **Remove** - Removed features or deprecated functionality
- [x] **Internal** - Internal changes (refactoring, tests, docs, etc.)

## Related Issues (Optional)
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## Breaking Changes
- [ ] This PR contains breaking changes

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-->

## Testing
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- [ ] Unit tests added/updated
- [ ] Integration tests added/updated  
- [ ] Manual testing performed
- [ ] No testing required (docs, internal refactor, etc.)

## Additional Notes
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Signed-off-by: Thomas McRoberts <tmcroberts@nvidia.com>

Author: tmcroberts97

crates/api/src/nvl_partition_monitor/mod.rs

@@ -860,11 +860,11 @@ impl NvlPartitionMonitor {
         HashMap<MachineId, Option<MachineNvLinkInfo>>,
         Vec<db::nvl_partition::NvlPartition>,
     )> {
-        // Only run validation once per hour.
+        // Only run once every 15 minutes.
         {
             let last_validation = self.last_nvlink_info_validation.lock().unwrap();
             if let Some(last_time) = *last_validation
-                && last_time.elapsed() < std::time::Duration::from_secs(3600)
+                && last_time.elapsed() < std::time::Duration::from_secs(900)
             {
                 return Ok((machine_nvlink_info, db_nvl_partitions));
             }