refactor(iam): promote supported_actions to const, extract CreatePolicyInput

[vieiralucas]

Summary

• Promote `IamService::supported_actions` from an inline 130-element `&[&str]` to a file-level `SUPPORTED_ACTIONS` const, matching the shape PR refactor(logs): extract subscription filter delivery and promote action list #336 used for logs. The method body is now one line.
• Extract `CreatePolicyInput::from_query` from `create_policy`. The parse + validate prologue (PolicyName, PolicyDocument, Path, Description, Tags + tag validation, MalformedPolicyDocument check) is now isolated from the state-mutation flow.

Audited and judged already-clean

• `list_policies` (49L): most of the body is sequential `validate_optional_*` calls, with a short filter+render tail. Splitting would just rearrange validate calls without improving readability.

Test plan

• `cargo fmt`
• `cargo clippy -p fakecloud-iam --all-targets -- -D warnings`
• `cargo test -p fakecloud-iam --lib` — 73 passed
• `cargo test --workspace --exclude fakecloud-e2e --exclude fakecloud-conformance`

---

Summary by cubic

Promotes IAM supported actions to a file-level SUPPORTED_ACTIONS const and extracts CreatePolicyInput to keep create_policy focused. No behavior changes; also fixes the conformance audit scanner to handle const-based supported_actions().

• Refactors

  • IamService::supported_actions() now returns SUPPORTED_ACTIONS (same shape used for logs in PR refactor(logs): extract subscription filter delivery and promote action list #336).
  • Added CreatePolicyInput::from_query to parse/validate inputs (PolicyName, PolicyDocument, Path, Description, Tags), leaving create_policy to mutate state.

• Bug Fixes

  • fakecloud-conformance audit scanner now supports const-backed supported_actions() by scanning the function body, resolving the const name, and parsing its definition; fixes the test failure.

^{Written for commit 26a7718. Summary will update on new commits.}

[cubic-dev-ai]

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