fix: applyLightData version boundary is 1.21.2, not 1.20.2 (crashes 1.21.1 at startup)

[Whisperlyric]

Problem

NEB 1.0.2 crashes dedicated servers and clients on MC 1.21.1 at startup with a
mixin injection failure (Critical injection failure / InvalidAccessorException
against ClientPacketListener).

Root cause

ClientPacketListener.applyLightData gained its trailing boolean parameter in
1.21.2, not 1.20.2:

Version	Signature
1.20.1 – 1.21.1	applyLightData(int, int, ClientboundLightUpdatePacketData) (method_38543)
1.21.2+	applyLightData(int, int, ClientboundLightUpdatePacketData, boolean)

The preprocessor boundary was written as //#if MC>=12002, so 1.21.1 (12101)
incorrectly selected the 4-arg form in three places:

• ClientChunkLightRecomputeMixin — 4-arg injection handler fails under defaultRequire: 1
• ClientPlayNetworkHandlerInvoker — 4-arg accessor throws InvalidAccessorException at apply time
• ModNetworking — cached-chunk replay calls the 4-arg invoker

Fix

• Boundary MC>=12002 → MC>=12102 in the two client mixins
• Split the ModNetworking call site on MC>=12102 (1.21.1 uses the 3-arg form)

Also included

buildAndGather gradle task: builds every version subproject and collects the
jars into build/libs, so a per-version breakage can no longer hide behind a
main-project-only build. All 8 subprojects verified to compile:
1.20.1, 1.21.1, 1.21.4, 1.21.6, 1.21.10, 1.21.11, 26.1, 26.2 → BUILD SUCCESSFUL.