XSLT: template selection resolves each match pattern once per transform via
a per-run MatchCache (the pattern's node set is computed once over the source
tree; selection becomes an identity lookup), replacing per-(node, template)
recompilation and full-tree re-walks. XSD identity validation: a per-run query
cache compiles each selector/field XPath once instead of at every visited
element. Schematron was verified to already store compiled queries. Behavior
unchanged (all suites green); a multi-template shape test over 300 nodes
guards the optimized path. MatchCache lives in its own file to keep the
transformer under the length cap.
Closes#112
