HPCC-11515 Under-caching of dynamic filename resolution

Cache any dynamic file lookups until the end of the current graph.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6044 from richardkchapman/roxie-cache-dynamic

HPCC-11515 Under-caching of dynamic filename resolution

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>