Sysmem should throw an error if we try to connect monomer to already occopied attachment point

[AlexeyGirin]

Steps to Reproduce

1. Go to Macromolecules mode - Flex mode
2. Load using paste from clipboard IDT type: CHEM1{[MCC]}|RNA1{R(U)P}$CHEM1,RNA1,1:R1-1:R2$$$V2.0

Actual behavior System load something

Expected behavior Error should occur - Can't connect to R2 attachment point of monomer index 1 of RNA1 - it is already occupied

Versions

• Ketcher Version 2.23.0-rc.1 Build at 2024-07-02; 08:57:41
• Indigo Toolkit Version 1.22.0-rc.1.0-g2bef0ce6c-wasm32-wasm-clang-19.0.0
• Windows 10 Pro
• Chrome Version 126.0.6478.127 (Official Build) (64-bit)

Issue found while testing - https://github.com/epam/Indigo/issues/1188

[AliaksandrDziarkach]

Planed to fix with variant monomers helm support.

[AlexeyGirin]

Re-CHECK

[split-ends]

Successfully verified: an error appears with the corresponding message:

Environment details: Ketcher Version: 2.25.0-rc.1 Build at 2024-09-03; 15:31:03 Indigo Version: 1.24.0-rc.1.0-gb8f099851-wasm32-wasm-clang-19.0.0 Chrome Version: Version 128.0.6613.113 (Official Build) (64-bit) Windows 11 Enterprise