Add CODEOWNERS file

[nethermind-oss-compliance]

📋 Add CODEOWNERS File

This PR adds a CODEOWNERS file template to help manage code ownership and review requirements.

🎯 What is CODEOWNERS?

The CODEOWNERS file defines who is responsible for code in this repository. When someone opens a pull request, the defined code owners are automatically requested for review.

✏️ How to customize this file:

1. For team ownership: Use @NethermindEth/team-name
2. For individual ownership: Use @username
3. For specific paths: Add patterns like docs/ @NethermindEth/docs-team

📖 Examples:

# Global owners (will be requested for all PRs)
* @NethermindEth/core-team

# Specific directory owners
/docs/ @NethermindEth/docs-team
/src/ @NethermindEth/development-team
*.md @NethermindEth/docs-team

# Individual file owners
package.json @username
README.md @NethermindEth/docs-team @username

🔗 Learn more:

• GitHub CODEOWNERS documentation

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Please review and update the CODEOWNERS file according to your team's needs before merging! 🚀

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.45%. Comparing base (fefe9ee) to head (7b5c321).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3118      +/-   ##
==========================================
- Coverage   73.46%   73.45%   -0.01%     
==========================================
  Files         305      305              
  Lines       34248    34248              
==========================================
- Hits        25159    25158       -1     
- Misses       7470     7473       +3     
+ Partials     1619     1617       -2     

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