fix: enforce UTC where time.Time is used

[technicallyty]

Description

Enforces UTC values when a raw time.Time value is used. timestamppb (both gogo, and google) uses UTC in conversions to and from time.Time. All of our state is stored using timestamppb, not time.Time, so we already have UTC across state. The only lingering problem would be batch denom formatting which is fixed with this PR (alongside expiration checks).

I pulled all batches from mainnet and double checked that formatting their batch denom using the stored start/end date results in the same batch denom stored in state.

Closes: n/a

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Author Checklist

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I have...

• included the correct type prefix in the PR title
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• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
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Reviewers Checklist

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I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #1194 (714ae65) into master (22622fb) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1194      +/-   ##
==========================================
+ Coverage   64.87%   64.95%   +0.07%     
==========================================
  Files         231      231              
  Lines       21709    21711       +2     
==========================================
+ Hits        14084    14102      +18     
+ Misses       6276     6254      -22     
- Partials     1349     1355       +6     

Flag	Coverage Δ
stable-codecov	64.95% <100.00%> (+0.07%)	⬆️

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