docs: Add FLUTE kernel analysis guide for kbit GEMM reference

Comprehensive technical analysis of the FLUTE (Flexible Lookup Table
Engine) kernel from arxiv 2407.10960, covering architecture, CUTLASS 3
implementation, vectorized LUT with bank-conflict duplication, Stream-K
work distribution, and detailed comparison with the bitsandbytes kbit
GEMM design across 10 dimensions (codebook lookup, weight packing,
scale format, work distribution, bit-width support, framework, tensor
cores, pipeline, offline preparation, and trade-off summary).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TimDettmers