Rust SDK: test coverage for admin.audit.search(filters)

[Mac-5]

Description
Add focused unit tests for admin.audit.search(filters) and admin.audit.export_csv(filters) (implemented in Issue #124) using a mocked HTTP transport — no live server, no database.

Scope guardrail: this PR must only touch files under sdks/rust/. Do not touch anything under src/ — read the handler referenced below only to learn the request/response contract.

Requirements and context

• Cover the happy path for both JSON search and CSV export modes.
• Test the cursor pagination edge case: the last page (where next_cursor is null) must be clearly distinguishable from a mid-stream page that happens to have zero results in the data array.
• Test that applying all optional filters (actor, action, from_date, to_date, entity_type) correctly serialises them as query parameters.
• Test that the admin key (not the public key) is sent.
• Depends on Issue Cursor Pagination Unit Tests #124.

Suggested execution

1. Fork the repo and create a branch
   git checkout -b feature/rust-sdk-test-coverage-for-adminauditsearch
2. Implement changes
   • Set up a mocked HTTP transport returning canned JSON and CSV responses.
   • Write happy-path tests for the JSON and CSV modes.
   • Write the last-page cursor edge case test.
   • Write the filter serialisation test.
   • Confirm cargo test is green with no network access required.
3. Test and commit
   • Run the crate's test command and confirm it's green
   • Example commit message: test(sdk): add coverage for admin audit search method

Guidelines

• Assignment required before starting
• PR description must include: Closes #125
• PR must only touch files under sdks/rust/
• Complexity: High (200 points) — Every issue in this Wave is tagged High — full points regardless of individual scope.

[DANeiraGarcia]

Hi hello, I would love to take on this testing issue as well.

I can implement the focused unit tests for admin.audit.search and admin.audit.export_csv using a mocked HTTP transport inside sdks/rust/. I will ensure we cover both JSON and CSV happy paths, proper query parameter serialization for all optional filters, admin key header verification, and the last-page cursor edge case.

Could you please assign this issue to me? Thanks!