The XPath expression with chained predicates on the ancestor axis was not
working correctly. For example:
  //*[@itemprop="author"][ancestor::*[@itemscope][1][@itemtype="Comment"]]

This expression should find all elements with @itemprop="author" whose first
@itemscope ancestor has @itemtype="Comment". However, it was returning 0
results instead of the expected elements.

Root cause:
1. ancestorQuery.table (deduplication table) was persisting across Evaluate()
   calls, preventing ancestors from being found for subsequent input contexts.
2. filterQuery.positmap (position map) was not being reset during Evaluate(),
   causing position tracking to be incorrect when the same predicate query was
   reused for multiple input nodes.

Fix:
- Reset ancestorQuery.table to nil in Evaluate() to ensure clean state for
  each evaluation
- Reset filterQuery.positmap to nil in Evaluate() to ensure clean state for
  each evaluation

These changes ensure that when a predicate query is evaluated multiple times
(once for each candidate node), the internal state is properly reset, allowing
the query to work correctly for each evaluation.

💁 Unit test by Mislav
🤖 Implementation by [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

When evaluating expressions like (//author)[last()], the last() function
was counting sibling nodes per-parent instead of counting the total nodes
in the grouped result set. This caused incorrect matches when group
members came from different parent nodes.

The fix ensures that b.firstInput is always set to the groupQuery in the
nodeGroup case, and adds handling for *groupQuery in the lastFuncQuery
conversion, using a cloned query to avoid consuming the shared input.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>