Fix item modifier classification on character import

[czarandy]

Description of the problem being solved:

Path of Exile 3.29 moved the crafted, fractured, and mutated classification fields under ItemMod.flags. The 3.29 import update reads those fields directly from ItemMod, so imported modifiers retain their text but lose their classification.

Read the nested flags object while retaining the existing fallback for older string/top-level modifier shapes.

Steps taken to verify a working solution:

• Added regression coverage using the 3.29 ItemMod response shape.
• Verified the test checks crafted, fractured, and mutated classifications after the imported item's raw rebuild/parse cycle.
• Ran git diff --check.
• Busted was not run locally because Docker Desktop's WSL integration and a local LuaJIT/Busted installation were unavailable.

Link to a build that showcases this PR:

N/A — character import data handling only.

Before screenshot:

N/A

After screenshot:

N/A