Port Turtlematic to Minecraft 1.21.1

[SirEdvin]

Migration

• Source branch: 1.20
• Target branch: 1.21
• Minecraft: 1.20.1 -> 1.21.1
• Java: 17 -> 21
• Loaders: Forge/Fabric -> NeoForge/Fabric

Major changes

• Merged all maintained 1.20 functionality before completing the port, including inspection monocle, husbandry points, forged automata capabilities, turtle chatter colors, capture/chunk-vial/item-suck fixes, and precomposited automata models.
• Migrated the build to Gradle 8.14, buildenv 0.9.0, NeoForge ModDevGradle, current Fabric Loom, and current 1.21.1 Broccolium/Tweakium/Peripheralium dependencies.
• Replaced the legacy Forge entrypoints, metadata, lifecycle, registration, datagen, and access-transformer setup with NeoForge equivalents while retaining the forge artifact ID.
• Regenerated Fabric and NeoForge resources using 1.21 singular paths and schemas.
• Added isolated Testiarium testmods, an aggregate gameTest task, XML/HTML reports, and Java 21 pull-request CI.

Compatibility

• Preserved mod IDs, item/entity/turtle-upgrade IDs, peripheral type names, config keys (including existing typo-bearing keys), saved-data names, Maven group, artifact IDs, and archive naming.
• Preserved consumed_entity_compound inside the 1.21 custom-data component so migrated 1.20 soul-progress items remain readable.
• Preserved turtlematic:* turtle upgrade type IDs on both loaders with a Turtlematic-owned NeoForge deferred registry.
• Testiarium and fixture artifacts remain test-only and are absent from production runtime graphs, POMs, and packaged JARs.

Verification

• ./gradlew :core:compileKotlin :core:compileJava
• ./gradlew :fabric:runData and ./gradlew :forge:runData; generated diffs inspected
• Fabric and NeoForge main/testmod compilation
• ./gradlew clean build --no-daemon
• timeout --foreground 600s ./gradlew gameTest --no-daemon: 2/2 tests passed on Fabric and 2/2 on NeoForge; fresh XML and HTML reports produced
• Fabric dedicated server reached Done, accepted stop, and saved all dimensions cleanly
• Fabric client initialized rendering and completed resource/atlas reload under xvfb-run; bounded timeout used
• Production dependency graphs, generated POMs, and packaged JAR contents inspected

CI and limitations

• Hosted GameTests run 29442394881 passed on the retry after an initial transient ModMenu Maven download truncation. The gametest-reports artifact (8354261171) was downloaded and verified to contain both loaders’ XML and HTML reports; each XML records 2/2 passing tests.
• No automated client world join was performed; the client smoke reached the title-screen/resource-loaded state and was terminated by the external timeout.
• No supported integration was intentionally removed or deferred.