uv run: --no-build-package <pkg> blocks one sdist build, not all

Pinning an old compiled release under a new interpreter (for example uv run --no-project --with scipy==1.16.3 on CPython 3.15) makes uv fall back to building the sdist. --no-build stops that but refuses sdists for every package, which also breaks old environments whose pure-Python dependencies only ship sdists. --no-build-package scipy refuses only that build: on uv 0.13.6 it fails at once on 3.15 ('has no usable wheels') and resolves normally on 3.12. Pair either flag with --python <version the release has wheels for>. uv run rejects pip's --only-binary.