fix(proxy): serialize LRU check-then-create in no-progress and compaction trackers

[devin-ai-integration]

Summary

noProgressTracker.recordAndDetect and compactionTracker.checkAndRecord each do a two-step Get+Add on their LRU. The LRU synchronizes individual calls but not the pair, so racing goroutines could orphan a freshly created fingerprintRing (losing recorded fingerprints and delaying loop detection) or evaluate the compaction drop check against stale prior state (false-positive detection). Both trackers now hold a sync.Mutex across just the Get+Add; ring.recordAndDetect runs outside the lock since fingerprintRing guards its own state.

Adapted from #472 by @rohith500; comments condensed per repo conventions.

Link to Devin session: https://app.devin.ai/sessions/840868be330a4e258f7325867c84caaf
Requested by: @steventohme

[devin-ai-integration]

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[greptile-apps]

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