Fix/v2 seeds program without seeds

[0x4ka5h]

Finding

seeds::program = ... without seeds = [...] was accepted in lang-v2, but it emitted no PDA verification at all. That silently disabled the intended seeds check.

Fix

This PR rejects seeds::program unless seeds is also present, matching v1 behavior and preventing the missing-verification path.

Regression tests added.

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Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (anchor-next@e056cc1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
lang-v2/derive/src/parse.rs	33.33%	4 Missing ⚠️
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Additional details and impacted files

@@              Coverage Diff               @@
##             anchor-next    #4826   +/-   ##
==============================================
  Coverage               ?   63.59%           
==============================================
  Files                  ?      126           
  Lines                  ?    13669           
  Branches               ?        0           
==============================================
  Hits                   ?     8693           
  Misses                 ?     4976           
  Partials               ?        0           

Flag	Coverage Δ
v2	63.59% <33.33%> (?)

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