bStats Custom Metrics

What changed

New API — EcoMetricsChart (eco-api)
Sealed Kotlin class exposing all bStats chart types as a clean, type-safe API. Supports SimplePie, AdvancedPie, DrilldownPie, SingleLineChart, MultiLineChart, SimpleBarChart, and AdvancedBarChart. Companion object provides @JvmStatic factory methods for Java compatibility.

EcoPlugin.getCustomCharts()
New opt-in method returning List. Returns empty list by default — zero breakage for existing plugins. Override to declare custom bStats charts submitted alongside standard metrics.

bStats vendoring via Gradle
Replaced the hand-rolled vendored Metrics.kt with a vendorBStats Gradle task that clones the official bStats-Metrics repo at a pinned tag (v3.2.1), relocates all sources from org.bstats → com.willfp.eco.libs.bstats, and prepends attribution headers. Output lands in build/generated/sources/bstats/ (not committed). Task is cached by version... re-runs only when bStatsVersion changes (or gradle clean). Solves a classpath conflict where MythicMobs bundles an unrelocated old bStats, which previously caused compile-time resolution to the wrong Metrics class.

Eco-specific charts (EcoImpl)
Eco now submits its own charts:

• data_handler — storage backend in use (yaml / mysql / mariadb / mongodb)
• loaded_eco_plugins — count of distinct loaded Eco-based plugins
• loaded_extensions — total extensions loaded across all Eco plugins
• antigrief_integrations — active antigrief plugins (AdvancedPie, share + count)
• custom_item_integrations — active custom item plugins (AdvancedPie)
• anticheat_integrations — active anticheat plugins (AdvancedPie)

getRegisteredIntegrations() added to AntigriefManager, AnticheatManager, CustomItemsManager
Mirrors the existing pattern from ShopManager. Used by the Eco metrics charts above.