docs(rpc): add DESCRIPTION to chain RPC methods

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• added descs to chain RPC methods

Reference issue to close (if applicable)

Part of #6460

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

Release Notes

• Documentation
  • Enhanced documentation for multiple JSON-RPC chain methods with detailed descriptions to improve API clarity and usability.

[coderabbitai]

Walkthrough

Adds DESCRIPTION string constants to 12 RpcMethod implementations in src/rpc/methods/chain.rs, covering both Filecoin.* and Forest.* namespaced methods. No request/response types or handle logic are modified.

Changes

Chain RPC Method Descriptions

Layer / File(s)	Summary
Add DESCRIPTION constants to chain RPC methods src/rpc/methods/chain.rs	Populates the DESCRIPTION field for ChainGetMessagesInTipset, SnapshotGC, ChainExport (both Forest and Filecoin namespaces), ChainExportStatus, ChainExportCancel, ChainExportDiff, ChainStatObj, ChainGetGenesis, ChainSetHead, ChainGetMinBaseFee, and ChainGetTipsetByParentState.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• Add DESCRIPTION to all RPC methods #6460: This PR directly contributes to the broader effort to add DESCRIPTION fields to all RPC method implementations across the codebase, specifically addressing the chain.rs methods listed in that issue.

Suggested reviewers

• hanabi1224
• sudo-shashank
• akaladarshi

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title 'docs(rpc): add DESCRIPTION to chain RPC methods' directly and clearly describes the main change—adding DESCRIPTION fields to chain RPC methods in the codebase.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chain-rpc-descs

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch chain-rpc-descs

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_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[akaladarshi]

Couple of comments otherwise LGTM

[akaladarshi]

Should we add some kind of differentiation between the ForestChainExport and ChainExport?.

[akaladarshi]

I think we should remove the parent base fee because the name suggests ChainGetMinBaseFee but the calculations uses the parent_base_fee.

Not sure for the correct thing here, so just pointing out.