Add storage operations to et_def.proto

[danmih-ixia]

##Summary

Extends the Chakra execution-trace schema (schema/protobuf/et_def.proto) with a typed model for storage operations so traces can represent I/O alongside compute and communication nodes.

• Adds three NodeType values — STORAGE_NODE, BATCH_NODE, CHECKPOINT_NODE — and an optional Node.storage field carrying a new StorageInfo message.
• StorageInfo is layered by StorageLevel (FS / PAGE / BLOCK / DEVICE) with a oneof detail { FsOp, PageOp, BlockOp }. The device layer intentionally has no typed detail and falls back to Node.attr.
• FsOp covers the POSIX syscalls whose byte traffic reaches storage (open/close/read/write/pread/pwrite/fsync/fdatasync/sync_file_range); metadata-only syscalls and mmap are deliberately out of scope.
• PageOp covers page-cache events that are causally attributable to an in-scope FS syscall (add_to_cache, dirty, sync/async readahead); background reclaim and mmap faults are out of scope.
• BlockOp covers bio/request lifecycle (Q/G/I/D/C) for the ops that flow from in-scope FS syscalls (READ, WRITE, FLUSH); discard/secure-erase/zone-management are out of scope.

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[Ricefrog]

recheck