Add Windows shared-memory transport — page-file-backed named CreateFileMapping + MapViewOfFile, mirroring the POSIX shm_open/mmap path and wire-compatible with the C++/Python/Go/Rust/Java peers.
Add size-gated pipe-vs-shm batch routing: batches below a byte threshold use the faster pipe, larger ones use shared memory. Threshold via VGI_RPC_SHM_MIN_BATCH_BYTES; default 128 KiB on POSIX, 1 MiB on Windows.