Preserve skill selection on character reimport

[mcagnion]

Fixes #8210 .

Description of the problem being solved:

When re-importing a character build (especially with "Clear Skills" enabled), Path of Building rebuilds socket groups from imported items/gems but loses user-selected skill state for matching groups.

Steps taken to verify a working solution:

• Re-imported a build with multiple socket groups after setting a non-default main socket group and active skill; confirmed the same main socket group and active skill are preserved after import.
• Marked specific socket groups as "Include in Full DPS", re-imported with "Clear Skills" enabled, and confirmed those flags were preserved on matching imported groups.
• Re-imported a build where socket groups/gems had changed (different sockets and gem setups) and confirmed the import completed without errors.