Replaces the unbounded defaultdict(asyncio.Lock) with an OrderedDict
guarded by _get_url_lock() and _evict_url_locks(). The cap is 4096
entries; LRU semantics keep the hot working set alive and oldest-
unlocked-first eviction trims back toward the cap on each new
insertion.
Eviction skips locks that are currently held — popping a lock that
a coroutine is mid-`async with` on would break its __aexit__. The
inner loop's evicted-flag handles the edge case where every
remaining entry is either the freshly inserted hash or held; in
that state the cap is briefly exceeded and the next insertion
retries, instead of looping forever.
Audit-Ref: SECURITY_AUDIT.md finding #5
Severity: Medium
pax
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