feat: value renderer for timestamp protos

[JimLarson]

Description

Closes: #12709

Part of Sign Mode Textual (ADR 050) implementation.

Renders Timestamp messages as RFC 3339 (simplified ISO 8601).

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Author Checklist

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I have...

• [ ] included the correct type prefix in the PR title
• [ ] added ! to the type prefix if API or client breaking change
• [ ] targeted the correct branch (see PR Targeting)
• [ ] 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
• [ ] included comments for documenting Go code
• [ ] updated the relevant documentation or specification
• [ ] reviewed "Files changed" and left comments if necessary
• [ ] confirmed all CI checks have passed

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[bot]]

Codecov Report

Merging #12860 (48fd2d0) into main (4fe7797) will decrease coverage by 0.13%. The diff coverage is 63.42%.

@@            Coverage Diff             @@
##             main   #12860      +/-   ##
==========================================
- Coverage   55.87%   55.74%   -0.14%     
==========================================
  Files         646      649       +3     
  Lines       54895    55022     +127     
==========================================
- Hits        30675    30671       -4     
- Misses      21762    21880     +118     
- Partials     2458     2471      +13     

Impacted Files	Coverage Δ
baseapp/abci.go	64.09% <0.00%> (-0.33%)	:arrow_down:
client/flags/flags.go	19.35% <0.00%> (-0.32%)	:arrow_down:
client/rpc/status.go	66.66% <ø> (ø)
client/utils.go	34.92% <0.00%> (ø)
server/config/config.go	38.00% <0.00%> (-1.59%)	:arrow_down:
server/rosetta/client_online.go	1.35% <0.00%> (ø)
server/swagger.go	0.00% <0.00%> (ø)
testutil/list.go	0.00% <0.00%> (ø)
types/result.go	76.74% <ø> (ø)
x/auth/tx/query.go	0.00% <ø> (ø)
... and 69 more

[JimLarson]

Reviewers PTAL - addressed all comments.

[JimLarson]

Added the rationale for fractional second truncation vs sortability.

Also confirmed 100% test coverage for the added code (except for the TODO for handling default proto messages).

[JimLarson]

Core reviewer - ready for your approval.

Changelog update intentionally omitted - we'll have one entry for the whole functionality.

[amaury1093]

I put automerge on.

This branch is out-of-date with the base branch

@JimLarson could you rebase/merge master into your branch? Or alternatively give write access to your branch, so that our bot can do it.