*: strenghten checks for fetching deposits from API

[KaloyanTanev]

Do a bit more verifications on the data fetched from the API. Nothing that was breaking initially though.

category: misc
ticket: none

[Copilot]

Pull request overview

This PR strengthens validation of deposit data fetched from the Obol API by deriving the ETH2 network from the lock file earlier and using it to BLS-verify partial and aggregated deposit signatures, reducing the chance that malformed or misleading API responses can poison the aggregated deposit signature.

Changes:

• Derive network from the cluster lock fork version before fetching deposits, and pass it through to the API client.
• Extend obolapi.Client.GetFullDeposit to accept network and BLS-verify each partial signature against its claimed share, plus verify the final aggregated signature.
• Update the Obol API deposit test to pass network into GetFullDeposit.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
cmd/depositfetch.go	Computes network earlier and passes it into full-deposit fetching.
app/obolapi/deposit.go	Adds network param and verifies partial + aggregated signatures; adds extra response sanity checks.
app/obolapi/deposit_test.go	Updates test call site to include network argument.

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[codecov]

Codecov Report

❌ Patch coverage is 73.80952% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.13%. Comparing base (c97cd83) to head (21bfe37).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
app/obolapi/deposit.go	75.67%	5 Missing and 4 partials ⚠️
cmd/depositfetch.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4541      +/-   ##
==========================================
+ Coverage   57.08%   57.13%   +0.04%     
==========================================
  Files         245      245              
  Lines       33003    33020      +17     
==========================================
+ Hits        18839    18865      +26     
+ Misses      11787    11779       -8     
+ Partials     2377     2376       -1     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud