Add from_timestamp_nanos

[Ali-Mirghasemi]

Add and implement from_timestamp_nanos and add unit test for it

Known issue

if you input i64::MAX function give you a valid datetime, but for i64::MIN it gives you None
i think it's because time unit is nanoseconds

Thanks for contributing to chrono!

If your feature is semver-compatible, please target the 0.4.x branch;
the main branch will be used for 0.5.0 development going forward.

Please consider adding a test to ensure your bug fix/feature will not break in the future.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c0f418b) 91.61% compared to head (82a80c9) 91.64%.
Report is 2 commits behind head on 0.4.x.

Additional details and impacted files

@@            Coverage Diff             @@
##            0.4.x    #1357      +/-   ##
==========================================
+ Coverage   91.61%   91.64%   +0.03%     
==========================================
  Files          38       38              
  Lines       17489    17553      +64     
==========================================
+ Hits        16023    16087      +64     
  Misses       1466     1466              

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[djc]

This should probably reuse the NANOS_PER_SEC const that we have defined somewhere.

[Ali-Mirghasemi]

NANOS_PER_SEC is in duration.rs mod and is inaccessible for me to use it, the solution is make them public for use

[jtmoon79]

NANOS_PER_SEC will be pub after #1351

[djc]

You can make it pub(crate) for this change.

[Ali-Mirghasemi]

So which one should i use for more compatibility with new commits?

• add pub(crate) in duration.rs
  or
• make them pub

[djc]

pub(crate), as said in my previous comment.

[djc]

Thanks!