test(auth): avoid i686 OAuth expiry overflow

Tien Rayrequested to merge
ray.tien0907/cli:fix/8198-i686-oauth-expiry into main

Summary

  • truncate the OAuth credential-helper fixture expiry to minute resolution
  • avoid platform-sized integer overflow in the i686 test expectation
  • keep production credential-helper behavior unchanged

Testing

  • Linux/386 RED: pipeline 2711419604, job 15570713637
  • Linux/386 GREEN: pipeline 2711453824, job 15570965041
  • focused OAuth subtest and full internal/commands/auth/login package pass
  • make test-changed passes 163 tests
  • complete post-commit lefthook run pre-push passes build, lint, generated-code checks, and changed tests
  • full local suite: 3918 pass, 8 skipped; only the two known linked-worktree config-path baseline tests fail

Closes #8198 (closed)

Prior implementation and credit: !2959 (closed) by @Ashutosh0x.

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