ci: use OIDC for codecov-action

[njzjz-bot]

Replace token-based authentication with OIDC (OpenID Connect) for codecov-action.
This is more secure and eliminates the need to manage upload tokens.

Changes:

• Add use_oidc: true to codecov-action configuration
• Add id-token: write permission at workflow level
• Remove token parameter from codecov-action (ignored when using OIDC)

This improves security and follows codecov-action best practices.

Generated by the task: njzjz-bot/njzjz-bot#25.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.23%. Comparing base (6509e59) to head (e41b653).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #99   +/-   ##
=======================================
  Coverage   59.23%   59.23%           
=======================================
  Files          56       56           
  Lines        6395     6395           
=======================================
  Hits         3788     3788           
  Misses       2607     2607           

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