Document require clauses in Lyte DSP docs

[jersmi7]

Summary

• document require clauses for slice-index helper functions in the quickstart and tutorial
• clarify that Audulus storage is persistent host storage, not the default place for large DSP buffers
• update the quickstart delay-line example to use a declared delay_mem global buffer and a write_delay helper with require clauses

Validation

• documentation-only change; reviewed rendered Markdown source/diff locally