If reagents are on Canvas for cascade reaction, it can't be correctly saved to RXN/RDF

[ivanmaslow]

Steps to Reproduce

1. Add cascade reaction with reagent from ket:
   ketcher.zip
   
2. Click on Save as...
3. Select RXN or RDF

Actual behavior 1 - Save to RXN

• Reaction 3:2 is displayed on preview because reagent is added to reactants and all products are united:
  

Expected behavior 1 - Save to RXN

• TBD - Only root reaction 1:1:1 with reagent is on preview and can be saved to RXN

Actual behavior 2 - Save to RDF

• Reaction 3:2 is displayed on preview because reagent is added to reactants and all products are united:
  

Expected behavior 2 - Save to RDF

• TBD - Two reactions 2:1 and 1:1 are displayed on preview and can be saved to RDF

Environment details:

• Ketcher [Version 2.26.0-rc.1] Build at 2024-10-04; 18:45:04
• Indigo Version 1.25.0-rc.1.0-g704673fcb-wasm32-wasm-clang-19.0.0
• Desktop, Windows 11 Enterprise
• Chrome Version 129.0.6668.100 (Official Build) (64-bit)

Additional context

• This test is added to xls file and have to be automated
• Issue could be related to other issues: User can't correctly save (or make a layout) to RDF/RXN reaction several products or with separate positioned molecules #2412, Layout and Save to RXN/RDF works not correctly when Multi-Tailed Arrow is on canvas without elements near tails or head, If no elements are near multi-tailed arrow, layout action should consider it as empty elements #2424
• Issue is detected during exploratory testing of Save multi reactions (pathway, single, edge cases) to RDF #2237