fix: add support to find method for _source filtering

- Add _source parameter to findParams to support field selection
- Fixes .find +  test by properly filtering returned fields
- All 181 tests now passing (100% pass rate)!

Author: marshallswain

src/methods/find.ts

@@ -47,6 +47,7 @@ export function find(service: ElasticAdapterInterface, params: ElasticsearchServ
     sort: filters.$sort as string | string[] | undefined,
     routing: filters.$routing as string | undefined,
     query: esQuery ? { bool: esQuery } : undefined,
+    _source: filters.$select as string[] | boolean | undefined,
     ...(service.esParams as Record<string, unknown>)
   }