Add support for parsing JSON timestamps from strings.

[rayhaanj]

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This change adds support for parsing string as (numeric) timestamps.

I had a look at the tests but was not sure where I should put the test for this feature, as the current logic to run tests is calling datetime::test_decodable_json which does not seem to be exercising the visitor path? Let me know where I should put them and I'll add the tests.

[esheppa]

I think it's probably worthwhile having a few tests to verify this works. They could just be placed at the bottom of the serde.rs file along with the other tests there.

[djc]

@rayhaanj would you have time to add a few tests?

[pitdicker]

I'll try to help get this PR ready. Added some very basic doctests. Good this was requested in previous reviews, as it didn't work yet :smile:. We now need to use deserialize_any instead of deserialize_i64.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.85%. Comparing base (0cfc405) to head (7f60d2c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #926      +/-   ##
==========================================
+ Coverage   91.80%   91.85%   +0.04%     
==========================================
  Files          37       37              
  Lines       18148    18181      +33     
==========================================
+ Hits        16661    16700      +39     
+ Misses       1487     1481       -6     

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[pitdicker]

Hmm, desertialize_any may not be the best thing to reach for:

Require the Deserializer to figure out how to drive the visitor based on what data type is in the input.

When implementing Deserialize, you should avoid relying on Deserializer::deserialize_any unless you need to be told by the Deserializer what type is in the input. Know that relying on Deserializer::deserialize_any means your data type will be able to deserialize from self-describing formats only, ruling out Postcard and many others.

[djc]

Yeah, I don't think we can/should restrict to self-describing formats only.

[pitdicker]

I've opened a question in the serde repo just in case. I think this is not going to work out, but no need to hurry closing this PR yet :smile:.

[pitdicker]

Closing as this approach seems like it is not going to work.