pyfdb: Always use array size specified by user

[ChrisspyB]

Description

It is currently not possible to read data from remoteFDB due to RemoteDataHandle.size() being NOTIMP. We should not have to call this function when a user specifies an array size.

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

🌈🌦️📖🚧 Documentation FDB 🚧📖🌦️🌈
https://sites.ecmwf.int/docs/dev-section/fdb/pull-requests/PR-261

[tbkr]

Changes look good to me, there are tests failing, though?

On second thought: this is breaking the shutil test case. We should double check whether this functionality is needed and come up with a solution for this.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.19%. Comparing base (62cc4bd) to head (2f6a24e).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #261   +/-   ##
========================================
  Coverage    71.19%   71.19%           
========================================
  Files          376      376           
  Lines        23762    23762           
  Branches      2478     2478           
========================================
  Hits         16918    16918           
  Misses        6844     6844           

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