fix (postgrest-js): preserve nullability when using JSON path (->) (#1635)

The JSON path resolver (JsonPathToType) stripped `null` using Exclude<T, null>
but never added it back to the resulting type. This caused `.select('col->a')`
to infer a non-nullable type even when the underlying JSON column was nullable.

Example:
  json_col: { a: string } | null
  .select('json_col->a')   // inferred `string` instead of `string | null`

This patch re-attaches `| null` when the root JSON column contains null,
ensuring correct type inference for nullable JSON columns and nullable
nested paths.

Fixes: #1635

Author: dev-hari-prasad

packages/core/postgrest-js/src/select-query-parser/utils.ts

@@ -618,7 +618,7 @@ export type JsonPathToAccessor<Path extends string> = Path extends `${infer P1}-
 export type JsonPathToType<T, Path extends string> = Path extends ''
   ? T
   : ContainsNull<T> extends true
-    ? JsonPathToType<Exclude<T, null>, Path>
+    ? JsonPathToType<Exclude<T, null>, Path> | null
     : Path extends `${infer Key}.${infer Rest}`
       ? Key extends keyof T
         ? JsonPathToType<T[Key], Rest>