fix(grey): fix Windows build errors across all build.rs and node.rs

[liuxiayu12]

Summary

Fix three categories of Windows build errors that prevented compilation on Windows.

1. build.rs path escaping (all 4 build.rs files)

PathBuf::display() emits Windows backslash separators which Rust's lexer interprets as escape sequences inside include_bytes! string literals (e.g. \b, \j, \s, \o).

Fix: Add include_path() helpers to build-javm and build-pvm that replace backslashes with forward slashes. All 4 build.rs files now use these helpers instead of .display():

• grey/crates/grey/build.rs
• grey/services/spec-tests/build.rs ? missed by fix(grey): fix Windows build errors in build.rs and node.rs #783
• grey/services/javm-guest-tests/build.rs ? missed by fix(grey): fix Windows build errors in build.rs and node.rs #783
• grey/crates/grey-bench/build.rs ? missed by fix(grey): fix Windows build errors in build.rs and node.rs #783

2. node.rs Unix-only signal handling

tokio::signal::unix is not available on Windows. The original code hardcoded SIGTERM, SIGUSR1, and SIGHUP signal registrations.

Fix: Wrap Unix-specific signal registrations in #[cfg(unix)] and provide std::future::pending::<()>() placeholders on non-Unix platforms so the select! arms compile but are simply never selected.

3. Comparison with #783

PR #783 fixed grey/build.rs and node.rs but missed the other 3 build.rs files that have the same .display() bug. This PR:

• Fixes all 4 build.rs files uniformly through the build-javm/build-pvm helper approach
• Adds include_path() to both build-javm and build-pvm crates (the latter is used by grey-bench)
• Uses &Path instead of &PathBuf to satisfy clippy

Testing

cargo build --workspace                                                          # passes on Windows
cargo clippy -p grey -p build-javm -p build-pvm --all-targets -- -D warnings    # 0 warnings
cargo test -p javm                                                               # 133 passed, 0 failed
cargo fmt --all -- --check                                                       # no diff

Note: This is a Windows compatibility fix with no functional changes to Unix builds.

[github-actions]

Genesis Review

Comparison targets:

• 313ee6bb (313ee6b)
• cb48a6fe (cb48a6f)
• 5b549442 (5b54944)
• 27e699fb (27e699f)
• afbc3e0d (afbc3e0)
• 37939ba1 (37939ba)
• b859d8f7 (b859d8f)

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