fix(node): prevent reranker from keeping process alive (#3270)

Fixes #3269.

## What I observed
Using a reranker in a hybrid query could keep the Node.js process alive
even after `table.close()` and `db.close()`.

## Root cause
The reranker callback bridge used a `ThreadsafeFunction` in referenced
mode, which can keep the event loop alive longer than intended.

## Minimal fix
- In `nodejs/src/rerankers.rs`, create the reranker callback TSFN in
weak mode (`.weak::<true>()`).
- Add a regression test in `nodejs/__test__/rerankers.test.ts` that
spawns a child process, runs a rerank query, and asserts the process
exits naturally.

## Validation
- Built Node bindings successfully.
- Ran targeted tests: `rerankers.test.ts` passes (including new
regression test).
- Pre-commit checks for changed files were run and clean.

nodejs/src/rerankers.rs

@@ -18,6 +18,7 @@ type RerankHybridFn = ThreadsafeFunction<
     RerankHybridCallbackArgs,
     Status,
     false,
+    true,
 >;
 
 /// Reranker implementation that "wraps" a NodeJS Reranker implementation.
@@ -32,7 +33,10 @@ impl Reranker {
     pub fn new(
         rerank_hybrid: Function<RerankHybridCallbackArgs, Promise<Buffer>>,
     ) -> napi::Result<Self> {
-        let rerank_hybrid = rerank_hybrid.build_threadsafe_function().build()?;
+        let rerank_hybrid = rerank_hybrid
+            .build_threadsafe_function()
+            .weak::<true>()
+            .build()?;
         Ok(Self { rerank_hybrid })
     }
 }