Flatten sei-cosmos go module into sei-chain

[masih]

Flatten the sei-cosmos go module into sei-chain tin reduce dependency management complexity and error-prone multi layer replace directives.

This is the final module and as a result also removes the now redundant go workspace.

Fixes PLT-6

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Feb 17, 2026, 12:55 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.04%. Comparing base (8fc1d5b) to head (4bf1969).

❗ There is a different number of reports uploaded between BASE (8fc1d5b) and HEAD (4bf1969). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (8fc1d5b)	HEAD (4bf1969)
sei-chain	1	0
sei-db	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2870       +/-   ##
===========================================
- Coverage   57.21%   49.04%    -8.18%     
===========================================
  Files        2093      681     -1412     
  Lines      171755    51556   -120199     
===========================================
- Hits        98276    25285    -72991     
+ Misses      64709    24100    -40609     
+ Partials     8770     2171     -6599     

Flag	Coverage Δ
sei-chain	?
sei-cosmos	49.04% <ø> (+0.89%)	⬆️
sei-db	?

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see 1593 files with indirect coverage changes

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