Refactor STS client operation modules

[GatewayJ]

Type of Change

• Refactor
• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Other: N/A

Related Issues

• N/A

Summary of Changes

• Reorganize src/sts/rustfs_client.rs by splitting admin/STS/S3/pool helper logic into dedicated submodules.
• Move shared request-signing and credential/response helpers into core_ops.rs and helpers.rs.
• Move RustfsAdminClient tests to src/sts/tests.rs while preserving existing coverage behavior.

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Passed make pre-commit (fmt-check + clippy + test + console-lint + console-fmt-check)
• Added/updated necessary tests
• Documentation updated (if needed)
• CHANGELOG.md updated under [Unreleased] (if user-visible change)
• CI/CD passed (if applicable)

Impact

• Breaking change (CRD/API compatibility)
• Requires doc/config/deployment update
• Other impact: N/A

Verification

git show --stat --oneline --no-patch

Additional Notes

• Commit created and pushed to my/feature/leader-election.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fix STS submodule paths

The new split-out STS modules are declared from inside src/sts/rustfs_client.rs, so Rust will look for them under src/sts/rustfs_client/admin_ops.rs (and likewise for s3_ops, pool_ops, sts_ops, core_ops, helpers, and the tests module). I checked the repository file list and these files were added as siblings under src/sts/, so the crate will fail to build with file-not-found module errors until the files are moved under src/sts/rustfs_client/ or each declaration is given the correct #[path = "..."].

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