Disable child metric registration under parent to prevent OOM

[sgrebnov]

🗣 Description

Temporarily disable child registration in child_with_tags() to prevent memory growth in long-lived VortexSession instances. The children Vec accumulates indefinitely with strong references never cleared.

Root cause:
VortexSession → VortexMetrics (root)
└─> children: RwLock<Vec> ← NEVER CLEARED

Each query creates child VortexMetrics (one per partition × files) that are registered with the session's root metrics and persist for the session lifetime, causing OOM in high-throughput scenarios.

Impact:

• Only bench-vortex is affected --show-metrics loses per-partition/per-file breakdown
• Root-level aggregated metrics still work
• No impact on EXPLAIN ANALYZE or production query execution

Vortex tracking issue:

• VortexMetrics Memory Growth: Children Accumulate Indefinitely in Long-Lived Sessions Resulting in OOM vortex-data/vortex#5946

🔨 Related Issues

🤔 Concerns

[Copilot]

Pull request overview

This PR temporarily disables child metric registration in the VortexMetrics::child_with_tags() method to prevent memory leaks caused by indefinite accumulation of child metrics in long-lived VortexSession instances. The change addresses an OOM issue in high-throughput scenarios where each query creates multiple child VortexMetrics instances (per partition and file) that persist for the session lifetime.

Changes:

• Commented out the line that registers child metrics with the parent, preventing memory accumulation
• Added a TODO comment with a link to the upstream tracking issue

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