Remove the httpr<0.5.2 pin in the Vespa integration once pyvespa releases the raise_for_status fix

integrations/vespa/pyproject.toml pins httpr>=0.4.0,<0.5.2 as a workaround. httpr is a transitive dependency of pyvespa; 0.5.2 added Response.raise_for_status, which makes pyvespa's raise_for_status() take its requests/httpx branch and let the resulting httpr.HTTPStatusError escape uncaught. The effect is that raise_on_not_found=False no longer suppresses 404s, so VespaDocumentStore.write_documents() raises for every new document and get_documents_by_id() raises instead of skipping missing ids.

Fixed upstream in unreleased as of pyvespa 1.2.4.

When a pyvespa release containing vespa-engine/pyvespa#1330 is out:

• drop the httpr pin from integrations/vespa/pyproject.toml (including the explanatory comment)
• raise the floor to that pyvespa version (currently pyvespa>=0.58.0)
• run the integration tests against a real Vespa to confirm 404 handling, since the failure only shows up there
• release a patch version of vespa-haystack

Context: PR #3761

After a pyvespa release containing vespa-engine/pyvespa#1330, start in integrations/vespa/pyproject.toml and review the httpr workaround and pyvespa version constraint. Run the Vespa integration tests against a real Vespa to confirm 404 handling, then release a patch version of vespa-haystack.