Cda support

[jeandet]

Most necessary work for CDA support in Speasy. This PR basically:

• changes Speasy time index from float to numpy datetime64(ns) breaks cache backward compatibility
• adds ISTP CDF files loading support
• introduces an Index object to provide simple dictionary like persistent storage (like cache but without eviction policy)
• forces CDA webservice impl to request CDF files
• provides bits to build CDA inventory (will mostly be used on proxy side)

Closes #43, closes #28

[codecov[bot]]

Codecov Report

Merging #47 (c405726) into main (b923e07) will decrease coverage by 5.53%. The diff coverage is 40.30%.

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
- Coverage   87.56%   82.03%   -5.54%     
==========================================
  Files          31       37       +6     
  Lines        1536     1681     +145     
  Branches      261      270       +9     
==========================================
+ Hits         1345     1379      +34     
- Misses        128      234     +106     
- Partials       63       68       +5     

Flag	Coverage Δ
unittests	?

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Impacted Files	Coverage Δ
speasy/core/index/__init__.py	0.00% <0.00%> (ø)
speasy/core/index/speasy_index.py	0.00% <0.00%> (ø)
speasy/webservices/amda/_impl.py	87.50% <ø> (ø)
...asy/webservices/cda/_inventory_builder/__init__.py	0.00% <0.00%> (ø)
...ces/cda/_inventory_builder/_xml_catalogs_parser.py	0.00% <0.00%> (ø)
speasy/webservices/cda/inventory.py	0.00% <0.00%> (ø)
speasy/webservices/cda/indexes.py	44.68% <44.68%> (ø)
speasy/core/cache/cache.py	82.25% <57.14%> (-9.90%)	:arrow_down:
speasy/products/variable.py	87.61% <77.41%> (-6.20%)	:arrow_down:
speasy/core/__init__.py	95.91% <90.00%> (-1.59%)	:arrow_down:
... and 12 more

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[lgtm-com[bot]]

This pull request introduces 10 alerts when merging c405726616f9299a12dee1dc7f64ecd798030878 into b923e073022d2343da2c9bb0aec6335a99b5f132 - view on LGTM.com

new alerts:

• 6 for Unused import
• 3 for Conflicting attributes in base classes
• 1 for Redundant assignment