* Metal shaders for efficient self attention on large sequences
Updated fast attention: GEMM-ified with Steel primitives
Uses flash attention 1 for scale correction
* more compiler silencing
* Address rebase issues
* Templatize kernel instantiation, revise cpu bindings
* Safer writes to output
* Permit batch size > 1
* Numerical fixes for sdpa self attention
* Re-enable test, remove unused variable
* add benchmarking script
* Disable sdpa prior to perf tuning, and simplify tests for per-patch CI
