_is_wheel_built() raises fatal ValueError for pre-built packages with build tags after #1273 #1358

After #1273, _is_wheel_built() crashes with a ValueError when a candidate wheel on a package index carries a build tag but the local configuration expects none.

ValueError: torch: changelog for version 2.11.0 is inconsistent.
Found build tag (2, '') but expected (0, '')

Pre-built packages return an empty build tag from PackageBuildInfo.build_tag() (_pbi.py:298-300) because we assume pre-built wheels come from PyPI and do not have a fromager build tag. When a separate package index (configured via wheel_server_url) hosts a wheel with a build tag > 0, the consistency check at build.py:548-554 raises.

This check existed before #1273 but was inside the broad try/except Exception block that caught it and treated it as a cache miss (return None). The refactoring in #1273 moved the candidate iteration loop outside that exception handler, making the previously-swallowed ValueError fatal.

How to reproduce

1. Configure a package as pre_built with a wheel_server_url pointing to a package index (e.g. torch with a GitLab PyPI registry)
2. Ensure that index has a wheel with a build tag > 0 (e.g. torch-2.11.0-2-cp312-cp312-linux_aarch64.whl)
3. Run a build that looks up that package:

   fromager build torch==2.11.0
   

4. The build fails with:

   ValueError: torch: changelog for version 2.11.0 is inconsistent. Found build tag (2, '') but expected (0, '')
   

Expected behavior: The build tag mismatch should be treated as a cache miss (log and skip the candidate), matching the pre-#1273 behavior.