v0.7.1

Axial 0.7.1

No API changes. This release re-cuts 0.7.0 under a new version number after the resumable-release
mechanism submitted duplicate NuGet symbol package uploads for 0.7.0, one of which nuget.org's
async validator flagged as failed even though the package itself published correctly. 0.7.0's
package and symbol IDs are already immutable on NuGet, so this release exists to give a clean,
unambiguous symbol package for the same content.

The publish-nuget job is now idempotent: it checks nuget.org before pushing each package and
skips anything already published, instead of re-running the full push loop (and re-submitting
symbol packages) on every retry.