Get Fields

Returns field definitions and their types for the specified project.

Context handling:

• If no context is provided (or an empty string), returns a flat mapping of field name → metadata for the default context.
• If a specific context name is provided, returns a flat mapping of field name → metadata for that context.
• If context is '*', returns a nested mapping of context_name → {field_name → metadata} containing fields from all contexts in the project.

Each field entry contains:

• data_type: The data type of the field (int, str, etc)
• field_type: Whether it's an entry, param, or derived_entry
• mutable: Whether the field can be modified
• unique: Whether the field enforces uniqueness
• created_at: When the field was first created
• artifacts: For derived entries, contains the equation
• description: The description of the field