Add cacheAsInfo() to read back what produced a cache file

A cacheAs file records the parameters of the call, the KorAP instance,
the index revision that instance's corpus had at the time and the version
of RKorAPClient that wrote it - which is what makes such a file worth
keeping next to a document, and until now there was no documented way of
getting at it. cacheAsInfo() returns the record, or NULL for a file
written before 1.4.0, which holds none.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Change-Id: If39a8e331a008529fda06d91862e1c498534d78a
diff --git a/NAMESPACE b/NAMESPACE
index 2fd3705..c059673 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -8,6 +8,7 @@
 export(bind_cols)
 export(buildWebUIRequestUrl)
 export(buildWebUIRequestUrlFromString)
+export(cacheAsInfo)
 export(ci)
 export(complete)
 export(defaultAssociationScoreFunctions)