gRPC: add tip timestamp to ChainPoint response

[carbolymer]

Changelog

- description: |
    gRPC: add tip timestamp to ChainPoint response
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  # - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
   - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...
# uncomment at least one main project this PR is associated with
  projects:
  # - cardano-api
  # - cardano-api-gen
   - cardano-rpc
  # - cardano-wasm

Context

• gRPC: Populate timestamp field in ChainPoint RPC responses #1133

Tested in:

• gRPC: Add chain tip timestamp check to gRPC test cardano-node#6493

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[Copilot]

Pull request overview

This PR fixes the previously-unpopulated timestamp field in gRPC ChainPoint responses by computing tip time from SystemStart + EraHistory, and updates the encoding/decoding utilities and tests accordingly.

Changes:

• Populate ChainPoint.timestamp in readParams / readUtxos by querying SystemStart and EraHistory and converting the tip slot to POSIX milliseconds.
• Extend mkChainPointMsg to accept a timestamp and add a corresponding decoder (utxoRpcChainPointMsgToChainPoint).
• Add a Hedgehog roundtrip property for ChainPoint including the timestamp field; add required time dependency.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cardano-rpc/src/Cardano/Rpc/Server/Internal/UtxoRpc/Query.hs	Queries SystemStart/EraHistory, computes tip timestamp, passes it into mkChainPointMsg.
cardano-rpc/src/Cardano/Rpc/Server/Internal/UtxoRpc/Type.hs	Adds timestamp field to mkChainPointMsg and introduces a corresponding decode helper.
cardano-rpc/test/cardano-rpc-test/Test/Cardano/Rpc/Type.hs	Adds a ChainPoint protobuf roundtrip property including timestamp.
cardano-rpc/cardano-rpc.cabal	Adds time as a library dependency.
cardano-api/src/Cardano/Api/Query/Internal/Type/QueryInMode.hs	Introduces slotToUTCTime conversion helper.
cardano-api/src/Cardano/Api/Query.hs	Re-exports slotToUTCTime.
cardano-api/src/Cardano/Api/Internal/Orphans/Misc.hs	Adds Error PastHorizonException instance to support error handling in callers.