Folia support

FAuction now officially supports Folia, in addition to Paper and its other forks.

• Every scheduled operation in the plugin — one-off async/sync work as well as the recurring auction expiration, cache refresh, pending currency delivery, and anti-spam cleanup tasks — now runs through a Folia-aware scheduler instead of the plain Bukkit scheduler, which Folia does not support.
• The unmaintained TaskChain dependency (co.aikar:taskchain-bukkit, no release since 2019-2021) has been fully removed.
• No configuration change required; behavior on regular Paper servers is unchanged.