Flatten Deeply Nested JSON

Problem

Given a parsed JSON value data consisting of nested dictionaries, lists, and scalar values, write a function that flattens it into a single dictionary. Use dot notation for dictionary keys and bracket notation for list indices, so nested values become path-based keys such as user.address.city or orders[0].id.

Constraints

• The input is valid parsed JSON containing only dictionaries, lists, strings, numbers, booleans, or None
• Nesting depth is at most 10^3
• Total number of scalar leaf values is at most 10^5
• Dictionary keys are non-empty strings and do not contain [ or ]