Fix overlapping chat links crashing the game

[Susko3]

Depends on:

• Cleanup chat link tests #25626

Partial fix for #25614. Partial because it doesn't produce the ideal parsing results. Ideal would be: "osu://edit/00:12:345 (1,2) - Test?"
If you think reaching the ideal is not required, the issue could be marked as completed.

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Fixes cases where the same string could be parsed into multiple overlapping links. This was caused by the faulty "Check for encapsulated links" logic.

This PR:

1. hardens LinkFlowContainer so it doesn't crash if overlapping links are provided (it'll ignore any overlapping links and log the problem)
2. changes the "encapsulated links" logic to be more general and handle all cases of overlapping links
   • I didn't verify/think about the maths behind the "encapsulated links" logic, but it clearly produces wrong results
   • overlapping links are already checked and accounted for in handleAdvanced(), so I took the new logic from there