feat(solana): validate chunk_count in assemble instructions

[mariuszzak]

Description

Add extra validations to avoid panics on [..chunk_count]

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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.
• Added relevant natspec and godoc comments.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.91%. Comparing base (a4a8191) to head (fb48bc9).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #860   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          27       27           
  Lines        1123     1123           
=======================================
  Hits         1122     1122           
  Misses          1        1           

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[vaporif]

chunk count should never be less than remaining accounts, it's ok if it's equal - means we have no preverifies

[vaporif]

comment