fix(vmm): retry access per physical mapping on Windows

[HUSRCF]

Fixes #635.

Problem

VmmArena::map_next reapplies access to the whole contiguous mapped prefix. That works around ROCm 7.2 Linux drivers which reject some valid non-zero subrange addresses, but Windows HIP 7.2 rejects the first prefix that spans two independently mapped physical allocations.

Fix

• keep the contiguous-prefix call as the primary path;
• on hipErrorInvalidValue only, retry access once per physical mapping;
• preserve all other access failures and the existing transactional cleanup path;
• add a CPU-only reproduction of the reported 4 MiB prefix / two 2 MiB mappings.

The fallback runs only while growing a VMM arena and only after the existing call fails, so successful Linux and Windows paths are unchanged.

Test plan

• cargo test -p hip-bridge --lib --locked — 17 passed
• scripts/fmt-changed.sh master
• git diff --check
• gfx1100 GPU1: HIP_VISIBLE_DEVICES=1 cargo run --release --locked -p hip-bridge --features lab --example vmm_arena_smoke -- 0 — all boundary growth, failure cleanup, teardown, and reload checks passed

cargo clippy -p hip-bridge --lib --locked -- -D warnings currently reaches three pre-existing warnings in hipfire-config/src/rocm.rs; this PR does not modify that file.

Windows ROCm 7.2 validation on the reporter's RX 7900 XTX remains required before marking ready.