Some memory optimisations

[ChrisspyB]

Avoid some copies and fix a strange buffer overflow when reading near the end of a file.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 80.28169% with 56 lines in your changes missing coverage. Please review.

Project coverage is 69.44%. Comparing base (5e41515) to head (925d71b).

Files with missing lines	Patch %	Lines
src/tools/gribjump-validate.cc	0.00%	13 Missing ⚠️
src/gribjump/gribjump_c.cc	0.00%	11 Missing ⚠️
src/gribjump/tools/EccodesExtract.cc	0.00%	11 Missing ⚠️
src/gribjump/remote/Request.cc	0.00%	8 Missing ⚠️
src/gribjump/remote/RemoteGribJump.h	0.00%	4 Missing ⚠️
src/gribjump/ExtractionData.cc	0.00%	2 Missing ⚠️
src/gribjump/api/ExtractionIterator.h	88.23%	2 Missing ⚠️
src/gribjump/LocalGribJump.cc	96.55%	1 Missing ⚠️
src/gribjump/compression/compressors/Simple.cc	90.00%	1 Missing ⚠️
src/gribjump/remote/RemoteGribJump.cc	80.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #49      +/-   ##
===========================================
+ Coverage    68.58%   69.44%   +0.86%     
===========================================
  Files           91       92       +1     
  Lines         4310     4340      +30     
  Branches       397      394       -3     
===========================================
+ Hits          2956     3014      +58     
+ Misses        1354     1326      -28     

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