[type:refactor] remove shenyu trie cache - #6303

…moval (#8117)

The Trie L2 cache was removed in #6303, but comments still described the
L1/L2/Trie lookup chain. Describe the actual matching path instead: the
bounded per-path match cache followed by default matching on a miss.

Also drop the remaining Trie references from maintained matching docs:
remove the orphaned L2 config comment, rename the L1 cache comments to
match cache, fix the trie wording in CommonPluginDataSubscriber and
LocalPluginController, and point HttpRouteParser at the current
matchSelector method.

Historical references in RELEASE-NOTES.md are kept.