[RNTuple] handle footer extension header links

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.40%. Comparing base (1579c30) to head (088efa6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #313 +/- ## ========================================== + Coverage 86.39% 86.40% +0.01% ========================================== Files 18 18 Lines 2447 2450 +3 ========================================== + Hits 2114 2117 +3 Misses 333 333 ```

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