System allow to load IDT mixed bases with index out of range declaration

**Steps to Reproduce**
1. Toggle to Macro - Flex mode
2. Load IDT from paste from clipboard way: `(B5:00653005)`

**Actual behavior**
System loads nucleoside successfully

**Expected behavior**
System throws an error - Index out of range

As per [requirements](https://github.com/epam/Indigo/issues/1619):

> Custom mixed bases are represented in ... (Ni:XXYYZZQQ), where i=1..4,

**Versions**
- Ketcher Version 2.25.0-rc.1 Build at 2024-09-03; 15:31:03
- Indigo Toolkit Version 1.24.0-rc.1.0-gb8f099851-wasm32-wasm-clang-19.0.0
- Chrome Version 128.0.6613.114 (Official Build) (64-bit)
- Win10

Reference issues: https://github.com/epam/Indigo/issues/1619

Reproduce the paste import in Macro - Flex mode with `(B5:00653005)` and inspect the IDT mixed-base parsing path. Compare the accepted index with the constraints in reference issue 1619; done means an out-of-range index is rejected with an error instead of loading successfully.

Written by the indexing model from the issue text.