chore: Remove dead duplicate `urlparse` in async `create_keys_public_url` (#750)

## Summary

The async `KeyValueStoreClientAsync.create_keys_public_url` assigned
`keys_public_url = urlparse(self._build_url('keys'))` early in the
method, but this value was unconditionally overwritten later by
`urlparse(self._build_url('keys', public=True))`. The sync counterpart
only has the single correct call — this was an asymmetric refactor
artifact.

No behavior change: the second assignment always won. Removing the dead
call eliminates a small wasted `_build_url`/`urlparse` on every call and
removes a latent foot-gun where code inserted between the two
assignments would silently see the non-public URL.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>