[PORT] - Add Minecraft 26.2 target

[CodeWithCharles]

Adds 26.2 as a seventh Stonecutter target. Also carries three fixes for bugs that already existed on main and got in the way.

Behaviour change worth reading before merging. On 26.2, /ssb above 15 now gives a command block instead of a container. 26.2 validates container contents strictly, so overstacked slots are silently replaced by EMPTY and you get an empty barrel. Overstacking is how the >15 range worked, and Mojang closed it. Below 26.2 nothing changes.

Commits, oldest first:

• Run malilib-api-processor on the client source set only. With splitEnvironmentSourceSets() the processor ran twice and wrote META-INF/kr1v/index.json at the same jar path both times. Loom <=1.16 silently dropped one, so our shipped 1.21.x jars have only ever contained the client half. Loom 1.17 hard-fails instead, which is how it surfaced. Every malilib-api usage is client side, so scoping the processor there fixes it at the source. Upstream issue: Multiple source sets not supported by annotation processor kr1viah/malilib-api#3
• Build CI on Java 25. build_reusable.yml still installed Java 21 while publish.yml was already on 25. The 26.x targets compile with --release 25.
• Fix /ssb command blocks never carrying their signal. SuccessCount was written to CUSTOM_DATA, which is item level data. BLOCK_ENTITY_DATA is what gets copied into the block entity on placement, so every /ssb command block has been outputting 0. Affects all seven versions, fixed on all seven.
• Bump Gradle to 9.5.1 and Loom to 1.17. Required by 26.2 per the Fabric announcement.
• Add Minecraft 26.2 target. Version file plus the API changes: dyed shulker box items collapsed into a ColorCollection, screen handling moved off Minecraft onto Gui, LevelRenderer.renderHitOutline replaced by the submit node model, and GameRenderer.getMainCamera renamed.

Tested in game on 26.2, 26.1.2 and 1.21.4 (ssb across all versions): mod loads, airplace outline renders in the right place, config menu and macro editor, macros run, //rstack, //colorcode, /ssb across the range.

One thing that is not new but was never written down anywhere: a command block only keeps its SuccessCount if you place it in creative with permission level 2. Vanilla restriction on command block data, applies on every version.

Important

Here's an attachement that contains the diff file to apply to the wiki :
diff.txt