Flatten Nested JSON Records

Problem

Given a Python object parsed from JSON, write a function that flattens it into a list of row dictionaries. Nested objects should be flattened using dot-separated keys, and arrays should be expanded by index using bracket notation such as items[0].id. If the input is a single object, return one flattened row; if it is a list of objects, return one flattened row per object.

Constraints

• 1 <= number of top-level records <= 10^4
• Total number of primitive leaf values across the payload is at most 2 * 10^5
• JSON values may be objects, arrays, strings, numbers, booleans, or null