Create RNA antisense strand and Create DNA antisense strand options are present in the menu for nucleoside without even one backbone connection

[AlexeyGirin]

Steps to Reproduce

1. Go to Macro - Flex mode (clean canvas)
2. Load from HELM: RNA1{R(A)}$$$$V2.0
   
3. Select all monomers on the canvas and call context menu for the nucleoside

Actual behavior
Create RNA antisense strand and Create DNA antisense strand options are present in the menu
Same problem on Sequence mode canvas

Expected behavior
Create RNA antisense strand and Create DNA antisense strand options are missing from the menu

As per requirement:

1. The minimal sense/antisense duplex consists of two "elements" connected via a hydrogen bond.

• An element can be a sugar connected to an "(anti)sense base" (R3-R1) that has one backbone connection;

Versions

• Ketcher Version 3.3.0-rc.1 Build at 2025-04-02; 09:36:56
• Indigo Version 1.31.0-rc.1.0-g859747ec7-wasm32-wasm-clang-19.0.0
• Chrome Version 135.0.7049.42 (Official Build) (64-bit)
• Win10

Issue found while testing: #6508