Avoid allocations in one-dimensional dispatch

[antono3]

Summary

• make enqueue_1d_after call OpenCL directly with stack-local work sizes
• remove the temporary global/local one-element slice allocations
• retain the existing validation, event ownership, synchronization, and public signature
• add pre-call validation coverage

Verification

• full convenience suite passes with released V 0.5.2
• vector-add runs with GCC and TinyCC
• formatter and whitespace checks pass