fix(solana): prefunded commitment block attack

[vaporif]

Description

refers https://github.com/zenith-security/2026-02-cosmos-labs/issues/2

---

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• Linked to GitHub issue with discussion and accepted design, OR link to spec that describes this work.
• Wrote unit and integration tests.
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• Review SonarCloud Report in the comment section below once CI passes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.91%. Comparing base (5cfe581) to head (90234bf).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #963   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          27       27           
  Lines        1123     1123           
=======================================
  Hits         1122     1122           
  Misses          1        1           

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[mariuszzak]

Could we have a more expressive type for signer_seeds? What do you think?

[vaporif]

yeah, we already have several of them everywhere but lets do it with separate PR replacing all of them

[srdtrk]

blocked by https://github.com/zenith-security/2026-02-cosmos-labs/issues/17 since fixing that might make this moot