Use fdb callback interface

[ChrisspyB]

No description provided.

[ChrisspyB]

Depends on ecmwf/fdb#63 , which updates the callback interface

[ChrisspyB]

TODO:

• Update fdb version requirement before merging.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.68%. Comparing base (6c2e44f) to head (cc3d323).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #37      +/-   ##
===========================================
+ Coverage    61.66%   61.68%   +0.02%     
===========================================
  Files           89       89              
  Lines         4596     4599       +3     
  Branches       500      500              
===========================================
+ Hits          2834     2837       +3     
  Misses        1762     1762              

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[ChrisspyB]

TODO:

* Update fdb version requirement before merging.

Cannot until FDB updates tags. Merging anyway