docs: add letdtcode as a contributor for code

[allcontributors]

Adds @letdtcode as a contributor for code.

This was requested by iluwatar in this comment

[skip ci]

[github-actions]

PR Summary

Adds @letdtcode as a contributor for code by updating the All Contributors configuration and README. This reflects a request from iluwatar to recognize code contributions.

Changes

File	Summary
.all-contributorsrc	Appended a new contributor entry for letdtcode (Thanh Nguyen Duc) with avatar URL, GitHub profile, and code contribution in the All Contributors list.
README.md	Bumped All Contributors badge count to 390 and added a new contributor cell for letdtcode in the contributors table.

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autogenerated by presubmit.ai

[github-actions]

✅ LGTM!

Review Summary

Commits Considered (2)

• f5cc5f7: docs: update .all-contributorsrc [skip ci]
• 94cd6e2: docs: update README.md [skip ci]

Files Processed (2)

• .all-contributorsrc (1 hunk)
• README.md (2 hunks)

Actionable Comments (0)

Skipped Comments (3)

• .all-contributorsrc [3551-3560]

  maintainability: "Add contributor entry for letdtcode"

• README.md [9-9]

  best_practice: "Add All Contributors badge in README"

• README.md [581-581]

  maintainability: "Add new contributor row to README table"

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud