[Refactor] Add TTL / version-stamp to MatchDataCache to guard against stale cached match results #7651

Background

PR #7055 optimized the positive cache reuse path in AbstractShenyuPlugin (moved defaultMatchSelector/defaultMatchRule into the null-cache branch so a reused cached MatchData takes effect). This fixes the reuse logic, but does not address a deeper safety gap in the underlying cache: the cached match result has no time-based expiry, so it is not guaranteed to be safe to reuse when a data-sync event is missed.

Root cause analysis

MatchDataCache (shenyu-plugin/shenyu-plugin-base) builds an L1 WindowTinyLFUMap keyed by (pluginName, path) plus an L2 trie. The L1 map is constructed with the three-arg form:

new WindowTinyLFUMap<>(capacity, maxSize, false)

• The boolean false only disables sampling-based admission; there is no expireAfterWrite.
• The four-arg constructor WindowTinyLFUMap(capacity, maxSize, false, expireAfterWrite) exists but is unused.
• Cache entries are written only when all conditions are URI_CONDITION_TYPE and matchRestful is false.
• Invalidation is fully event-driven: CommonPluginDataSubscriber calls removeSelectorData / removeRuleData / cleanXxx on selector/rule/plugin add/update/delete, plus LocalPluginController local mode.

Risk

Because eviction is size-only, if a data-sync event (websocket / nacos / zookeeper notification) is dropped, delayed, or processed out of order, a stale selectorData/ruleData can remain in the cache indefinitely — there is no time-based self-healing. Under selector/rule churn this can cause:

• Wrong selector/rule matched → incorrect routing / plugin skip / wrong upstream chosen.
• Negative-cache sentinels (removeEmptyXxx) similarly never expire.

Proposal

Add a bounded TTL to the cached match result:

1. Use the existing four-arg WindowTinyLFUMap(capacity, maxSize, false, expireAfterWrite) with a short window (e.g. 30–60s), OR
2. Embed a data-version / epoch stamp in the cache key/value and invalidate when the plugin data version changes, OR
3. Both: TTL as a safety net + version stamp for precise invalidation.

The TTL should be configurable (e.g. via shenyu.match.cache.ttl) with a sensible default, and documented as a trade-off between reuse hit-rate and staleness window.

Acceptance criteria

• Stale entries are auto-purged after the TTL even if no data-sync event arrives.
• Negative-cache sentinels respect the same TTL.
• TTL is configurable with a safe default; hit-rate regression verified by existing match tests.
• No behavior change for the normal (event-driven) invalidation path.

Related: #7055