Fix Extrinsics codification

[MiguelDD1]

It fixes the serialization of AppUncheckedExtrinsic, in order to be aligned with expected format from subxt.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (6b1fd23) 54.57% compared to head (31eb6b8) 54.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   54.57%   54.56%   -0.01%     
==========================================
  Files          43       43              
  Lines        6133     6134       +1     
==========================================
  Hits         3347     3347              
- Misses       2786     2787       +1     

Impacted Files	Coverage Δ
...imitives/avail/src/asdr/app_unchecked_extrinsic.rs	71.47% <0.00%> (-0.25%)	⬇️

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