[Staging] Address Lucene backend review feedback

[nvzm123]

Warning

Temporary review/staging PR against the historical PR NVIDIA#2624 branch. This is
not a merge candidate; the focused five-PR split plus its independent Java
prerequisite is the intended merge path.

Summary

• move the PyLucene builder beside its owning conda recipe;
• centralize repeated runtime/artifact identifiers and remove transient links
  from production diagnostics;
• move default and failed-result policy behind the generic backend contract;
• remove Lucene-specific examples and branches from the central runner; and
• replace recipe-local inline assertions with an installed-package smoke test.

Validation

• focused Lucene suite: 165 passed;
• broader cuVS Bench suite: 313 passed, with expected optional skips and two
  pre-existing /data dry-run cases deselected;
• builder shell syntax, Python compilation, and git diff --check: passed.

These changes are being transferred to their respective owners in the split
series rather than merged as an additional patch on the oversized branch.