Add LIT (Limit If Touched) to OrderType enum

[Copilot]

Parsing IB Flex reports containing LIT (Limit If Touched) orders raises ValueError: 'LIT' is not a valid OrderType. This order type appears in 2025 flex reports but was absent from the enum.

Changes

• ibflex/enums.py: Add LIT = "LIT" to OrderType
• tests/test_types.py: Add TradesOrderLITTestCase covering orderType="LIT" → enums.OrderType.LIT

class OrderType(str, enum.Enum):
    ...
    MIT = "MIT"
    LIT = "LIT"  # Limit If Touched

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