Modeling - Fix array indexing bug in IntAna_IntQuadQuad::NextCurve method (#703)

Modeling - Fix array indexing bug in IntAna_IntQuadQuad::NextCurve method (#703)

Fixed a critical indexing bug in IntAna_IntQuadQuad::NextCurve where the
  method incorrectly used nextcurve[I] instead of nextcurve[I-1] for
  determining the theOpposite parameter.
This mismatch between 1-indexed API
  parameters and 0-indexed array access could lead to out-of-bounds memory
  access and incorrect curve connectivity determination.

Changes:
  - Fix IntAna_IntQuadQuad::NextCurve to use consistent I-1 indexing for both
   condition check and return value
  - Add comprehensive GTests covering NextCurve functionality, edge cases,
  and performance
  - Ensure proper error handling for invalid curve indices