## Summary

- Add a runtime-selected scheduler adapter for the Spigot plugin.
  - Standard Bukkit/Spigot servers retain the existing Bukkit scheduler behavior.
  - Folia and Canvas use each player's entity scheduler, allowing scheduled
    player work to follow the player between regions.
- Route the delayed join handler and plugin-message send through the adapter.
- Generate `folia-supported: true` in `plugin.yml`.
- Add Thowan to the generated plugin authors list.
- Upgrade the Gradle wrapper and plugin.yml generator.

## Build version rationale

`net.minecrell.plugin-yml` was updated from 0.5.2 to 0.6.0 because 0.5.2
does not expose the `foliaSupported` DSL property required to generate
Folia's `plugin.yml` support flag.

The Gradle wrapper was updated from 7.4.2 to 7.6.4 because plugin-yml 0.6.0
uses Jackson 2.15.2. Gradle 7.4.2 cannot process that dependency's
multi-release Java 19 classes (`Unsupported class file major version 63`);
Gradle 7.6.4 supports them.

This does not change the Java compatibility targets: `common` remains Java 8
and `spigot` remains Java 11.

Updated spigot and sponge build.gradle.kts to match the latest release version+differentiate the spigot version