Function write_lockfile 

pub fn write_lockfile(lockfile: &Lockfile) -> String

Render a lockfile to JSON.

Determinism guarantees:

• Top-level keys: lockfileVersion, manifestHash, entries (in that order, fixed by the Lockfile struct’s field order).
• entries map keys: alphabetical, courtesy of BTreeMap.
• Each entry’s agents and dependencies arrays: alphabetical.
• Trailing newline (POSIX-friendly diffs).