Fix some configuration cache violations

[lukebemish]

This PR fixes two configuration cache violations:

• The shouldSign convention no longer has serialization issues
• The maven publication reporting service is now fed proper publication data even when the transient task.publication fields are not present when restoring from cache, by capturing the relevant values from them in providers.

Testing locally, this is enough to allow building and locally publishing NeoGradle with configuration caching enabled.

[lukebemish]

No clue how version bumps work for this project so leaving that out. I'll also note that maty seems to have done - entirely independently - the same fix as I did to the first violation on the fix/configcache branch, though this also fixes the second issue which is a bit... weirder, thanks to gradle's weirdness with config cache and publications.