Derive Hash on tendermint::Time again

[kevinji]

This reintroduces #1054 after it was removed in #1203.

I believe there was no concern in having Time derive Hash so it seems fine to re-apply this change.

• 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/

[codecov-commenter]

Codecov Report

Merging #1278 (18ba722) into main (d550fdf) will not change coverage.
The diff coverage is 100.0%.

❗ Current head 18ba722 differs from pull request most recent head 95acaaa. Consider uploading reports for the commit 95acaaa to get more accurate results

@@          Coverage Diff          @@
##            main   #1278   +/-   ##
=====================================
  Coverage   64.1%   64.1%           
=====================================
  Files        271     271           
  Lines      24306   24306           
=====================================
  Hits       15589   15589           
  Misses      8717    8717           

Impacted Files	Coverage Δ
tendermint/src/time.rs	97.6% <100.0%> (ø)
tendermint/src/block/commit_sig.rs	78.4% <0.0%> (-2.0%)	⬇️
rpc/src/client/transport/router.rs	81.9% <0.0%> (-0.7%)	⬇️
testgen/src/header.rs	83.5% <0.0%> (-0.6%)	⬇️
testgen/src/vote.rs	85.8% <0.0%> (+0.8%)	⬆️
light-client-verifier/src/types.rs	39.0% <0.0%> (+0.8%)	⬆️

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