fix(xdc): prevent InvalidOperationException in XdcPool.EndRound

[andrewshab3]

Changes

The original code iterated over _items.Keys while calling _items.Remove() inside the loop.This causes InvalidOperationException: Collection was modified; enumeration operation may not execute at runtime when any item matches the removal condition.

Types of changes

What types of changes does your code introduce?

• Bugfix (a non-breaking change that fixes an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
• Optimization
• Refactoring
• Documentation update
• Build-related changes
• Other: Description

[andrewshab3]

@LukaszRozmej @ak88 sorry, can you check please?

[cicr99]

Hi @andrewshab3, current version supports Dictionary.Remove during enumeration without throwing (see here in docs).
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