Documents the safety contracts for:
- read8/read16/read32/read64: bounds check guarantees offset + N <= size
- write8/write16/write32/write64: same; volatile write must not reorder
- read_bytes/write_bytes: per-byte iteration with bounds check invariant
- Drop::drop munmap: ptr produced by successful fmap, Drop owns mapping
- Send/Sync impls: process-local mapping, kernel guarantees no aliasing
Note: read8 was already documented in a prior commit.
vasilito
6debc2582e