SPMD API overhaul: gather/scatter, job & packaging updates

- ISPMDLane: add MaskGather, MaskStore, Scatter, MaskScatter; update MaskLoad/Gather signatures for hardware parity
- WideLane/ScalarLane: implement new methods with HW/fallback logic
- MathV: gather/mask-gather now delegate to lane methods
- Vector2/3/4: add CompressStore, Scatter, MaskScatter
- SPMD jobs/tests/README: migrate to new APIs for correctness
- Use Unsafe.BitCast instead of Unsafe.As/AsRef
- Add SPMDUtility for gather index extraction
- Job system: add ICustomJob<TSelf>, ScheduleCustom overload
- FreeList concurrency obsolete; always thread-safe
- NuGet: include LICENSE/README, set license/readme in .csproj
- Docs: update SPMD usage, clarify safety notes
- Minor: doc fixes, CompressStore test improvements

Misaki.HighPerformance.Jobs/JobScheduler.cs

@@ -767,7 +767,6 @@ public sealed unsafe partial class JobScheduler : IDisposable
     /// <returns>A <see cref="JobHandle"/> that can be used to track the completion of the scheduled job. Returns <see cref="JobHandle.Invalid"/> if the job data allocation fails.</returns>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public JobHandle ScheduleCustom<T>(ref readonly CustomJobDesc<T> jobDesc, bool preferLocal, params ReadOnlySpan<JobHandle> dependencies)
-        where T : struct
     {
         if (jobDesc.jobRanges.totalIteration == 0 || jobDesc.jobRanges.batchSize == 0 || Unsafe.IsNullRef(in jobDesc.data))
         {
@@ -793,6 +792,16 @@ public sealed unsafe partial class JobScheduler : IDisposable
         return CreateJobHandle(ref jobInfo, preferLocal, dependencies);
     }
 
+    /// <summary>
+    /// Schedules a custom job for execution with user-defined <see cref="JobInfo"/>.
+    /// </summary>
+    /// <param name="jobDesc">The description of the custom job to be scheduled, containing all necessary information for execution.</param>
+    /// <param name="dependencies">A collection of <see cref="JobHandle"/> representing the dependencies that must be completed before this job can begin.</param>
+    /// <returns>A <see cref="JobHandle"/> that can be used to track the completion of the scheduled job. Returns <see cref="JobHandle.Invalid"/> if the job data allocation fails.</returns>
+    /// <returns></returns>
+    public JobHandle ScheduleCustom<T>(ref readonly CustomJobDesc<T> jobDesc, params ReadOnlySpan<JobHandle> dependencies)
+        => ScheduleCustom(in jobDesc, false, dependencies);
+
     /// <summary>
     /// Combines multiple job dependencies into a single <see cref="JobHandle"/>.
     /// </summary>