After #302 cached the document node list, the following and preceding axes still
materialized the entire following/preceding span (Array(slice), one Node copy
with a slow side-table retain per node) before the step's node test filtered it.
For a rare-target query that copy is almost entirely waste.
Fuse the node test into the walk: apply the test to the cached document-order
slice directly, so a node the test rejects is never copied out of the shared
list, only the matches are materialized. The selected nodes and their order are
unchanged (the test is the same compiled node test the general axis path used).
The 200-context following:: query over a 20k-element document drops from ~9s
(post-#302) to ~6s, ~2.6x below the original ~16s. The full suite, the W3C
XPath/XSLT and Apache Xalan corpora, and the WASM build stay green;
FollowingPrecedingAxisTests gains a fused-name-test case.
Mihaela Mihaljevic
0405850d6b