fix(ci): prefetch state computation snapshots to make codecov less flaky

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• New Features

  • Added state snapshot file discovery and retrieval from remote storage.
  • Implemented concurrent processing of state snapshots to streamline test workflows.
  • Enhanced state snapshot management with batch validation and error handling.

• Chores

  • Added justjson library dependency.

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[coderabbitai]

Walkthrough

The changes add remote state snapshot handling by introducing a justjson dependency and implementing functionality to fetch and list state snapshot files from remote storage, while integrating this into the existing test snapshot workflow pipeline.

Changes

Cohort / File(s)	Summary
Dependency Management Cargo.toml	Adds justjson v0.3 as a direct dependency in the workspace
State Snapshot Utilities src/state_manager/utils.rs	Introduces DO_SPACE_ROOT constant, adds get_state_snapshot_file() to fetch specific snapshots and list_state_snapshot_files() to query available snapshots from remote storage; updates snapshot retrieval to use the new helper function; adds test coverage for listing and file retrieval functionality
Dev Subcommand Integration src/dev/subcommands/mod.rs	Adds new fetch_state_tests() async function that lists and processes state snapshot files concurrently with per-task error handling; extends fetch_test_snapshots workflow to invoke fetch_state_tests() before existing fetch_rpc_tests() call

Sequence Diagram

sequenceDiagram
    participant FTS as fetch_test_snapshots()
    participant FST as fetch_state_tests()
    participant LSF as list_state_snapshot_files()
    participant GSF as get_state_snapshot_file()
    participant Remote as Remote Storage
    participant FRT as fetch_rpc_tests()

    FTS->>FST: invoke fetch_state_tests()
    FST->>LSF: request available snapshots
    LSF->>Remote: query DO_SPACE_ROOT/index
    Remote-->>LSF: return snapshot list
    LSF-->>FST: return .car.zst files
    
    par Process Snapshots
        FST->>GSF: fetch snapshot 1
        GSF->>Remote: download file
        Remote-->>GSF: file content
        GSF-->>FST: return local path
    and
        FST->>GSF: fetch snapshot 2
        GSF->>Remote: download file
        Remote-->>GSF: file content
        GSF-->>FST: return local path
    end
    
    FST-->>FTS: complete with errors logged
    FTS->>FRT: invoke fetch_rpc_tests()
    FRT-->>FTS: complete

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• LesnyRumcajs
• sudo-shashank
• akaladarshi

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: prefetching state computation snapshots to improve codecov reliability, which is directly supported by the new fetch_state_tests() function and snapshot handling utilities added in the PR.

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✨ Finishing touches

• 📝 Generate docstrings

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[codecov]

Codecov Report

❌ Patch coverage is 62.26415% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.74%. Comparing base (a23d136) to head (b7c5a17).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dev/subcommands/mod.rs	0.00%	14 Missing ⚠️
src/state_manager/utils.rs	84.61%	1 Missing and 5 partials ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/state_manager/utils.rs	82.24% <84.61%> (+0.11%)	⬆️
src/dev/subcommands/mod.rs	25.00% <0.00%> (-6.38%)	⬇️

... and 3 files with indirect coverage changes

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