fix(cache): add structured debug log for each cache eviction (#737)

[Alaka-ibr]

Closes #737

The in-memory creator list cache evicts entries on TTL expiry and capacity overflow, but neither case was logged with the structured fields needed to tune cache size and TTL in production. This PR adds a debug-level structured log at each eviction site with a consistent field schema.

Changes

src/modules/creators/creators.cache.ts

• TTL expiry eviction (both the prune loop and the stale-on-read path in getCachedCreatorList): now logs with reason: 'ttl_expired' and includes cache_key, cache_size_after, and evicted_at.
• Capacity overflow eviction in pruneCreatorListCache: now logs with reason: 'capacity_overflow' and includes the same fields.
• The delete() call is performed before the log statement so cache_size_after reflects the post-eviction map size.
• All eviction logs are emitted at debug level, suppressed at the default info level in production.

src/modules/creators/creators-cache-eviction-log.test.ts [NEW]

Seven unit tests covering all four acceptance criteria:

Test	Criteria
emits debug log with reason ttl_expired when a stale entry is read	TTL expiry fields
cache_size_after reflects the size after eviction	post-eviction size
evicted_at is a valid ISO 8601 timestamp	timestamp format
log level is debug	log level
emits debug log with reason capacity_overflow when cache exceeds max entries	overflow fields
cache_size_after reflects the size after the overflow eviction	post-eviction size
evicted_at is a valid ISO 8601 timestamp on overflow eviction	timestamp format

Log schema

{
  "msg": "Creator list cache eviction",
  "event": "creator_list_cache_eviction",
  "cache_key": "creators:limit=20:offset=0:sort=createdAt:order=desc",
  "reason": "ttl_expired | capacity_overflow",
  "cache_size_after": 249,
  "evicted_at": "2026-08-23T20:59:00.000Z"
}

[Alaka-ibr]

Done with this, please review

[Chucks1093]

LGTM!

[Chucks1093]

This is a very clean implementation. Adding the structured debug logs with the eviction reason and cache size after deletion will make production debugging so much easier going forward.