fix(node): avoid PATH-dependent shell execution in musl probe

[NeerajCodz]

Motivation

• The Node loader's fallback in isMusl() used child_process.execSync('which ldd'), which invokes a shell and resolves which through PATH, enabling local PATH-poisoning to execute attacker-controlled binaries during module import on older Node runtimes.
• The musl probe is invoked during Linux native binding selection, so importing the generated N-API loader could trigger this command execution.

Description

• Replace the PATH-dependent execSync('which ldd') probe with a safe fixed-path check that inspects /usr/bin/ldd and /bin/ldd using existsSync and readFileSync in bindings/node/index.js.
• Preserve the existing fallback behavior by returning true on probe errors and leave the remaining loader selection logic unchanged.

Testing

• Ran node --check bindings/node/index.js to validate the modified file is syntactically valid, and it succeeded.
• No other automated tests were modified or required for this change.

---

Codex Task