Tendermint: Added unix_timestamp and unix_timestamp_nanos method in Time struct.

[scalalang2]

close #1175

I thought it would be easier to write code with other time libraries such as chrono if it porivided a unix timestamp

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[scalalang2]

I applied all feedbacks for now.

[scalalang2]

Broken unit test is not related with this updates.
I'll fix it in another pull request.

[mzabaluev]

Looks good to me.

[thanethomson]

Please rebase this against the main branch - we no longer use the master branch, as per #1179.

[scalalang2]

Thanks for your feedback!
If the rebasing is done, i'll inform to you :)

The base branch was changed.

[scalalang2]

I rebased it, thanks for all reviews 👍

[codecov-commenter]

Codecov Report

Merging #1176 (5cd5f6b) into main (3c28657) will increase coverage by 0.0%.
The diff coverage is 84.2%.

@@          Coverage Diff          @@
##            main   #1176   +/-   ##
=====================================
  Coverage   64.2%   64.2%           
=====================================
  Files        244     244           
  Lines      21345   21364   +19     
=====================================
+ Hits       13715   13728   +13     
- Misses      7630    7636    +6     

Impacted Files	Coverage Δ
tendermint/src/time.rs	97.6% <84.2%> (-1.0%)	⬇️
testgen/src/vote.rs	84.0% <0.0%> (-0.9%)	⬇️
testgen/src/commit.rs	90.6% <0.0%> (-0.7%)	⬇️
testgen/src/header.rs	82.9% <0.0%> (-0.6%)	⬇️
light-client-verifier/src/types.rs	38.4% <0.0%> (-0.3%)	⬇️
tendermint/src/node.rs	63.9% <0.0%> (+0.1%)	⬆️

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