SI-8: Eliminate all unwraps from the REST API client package

[josecelano]

Description

Eliminates all .unwrap() calls from the torrust-tracker-rest-api-client package as specified in issue #1969.

Changes

• 11 public ApiHttpClient methods now return Result<Response, ClientError> instead of panicking
• post_empty(), post_form(), get(), get_request(), get_request_with_query() — all return Result
• Free function get() — returns Result
• 4 provably infallible conversions — use .expect("infallible: ...") with rationale (headers_with_request_id, headers_with_auth_token, auth token inserts in get_request_with_query_result)
• All callers updated — contract tests use .unwrap() (test code), E2E runner propagates with ? (production code)
• Pre-existing clippy fix — redundant_else in http_health_check.rs

Design Decisions

Per discussion (2026-07-13):

• Two-phase approach: Phase 1 changes signatures and makes callers compile. Phase 2 evaluates each caller site to decide between .unwrap(), .expect(), or ?.
• All public functions return Result: No panicking public API surface remains.

Verification

• All ApiHttpClient public methods return Result<Response, ClientError>
• No bare .unwrap() calls remain (only .expect("infallible: ..."))
• Pre-commit checks pass (machete, deny, linter, doc-tests)
• cargo check --tests --workspace passes
• cargo clippy --lib -p torrust-tracker-rest-api-client passes

Closes #1969

[Copilot]

Pull request overview

This PR implements SI-8 by making the low-level REST API HTTP client (torrust-tracker-rest-api-client) return Result instead of panicking, and updates downstream callers (contract tests, integration tests, and the qBittorrent E2E wrapper) to compile against the new signatures.

Changes:

• Updated ApiHttpClient public request methods (and the free get helper) to return Result<Response, ClientError> rather than unwrapping.
• Updated REST API server contract tests and integration tests to explicitly unwrap/expect the new Result in test code.
• Propagated errors in the qBittorrent E2E tracker client wrapper with ?, and applied a small clippy-driven cleanup in http_health_check.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/servers/api/contract/stats/mod.rs	Adapts integration helper to the new fallible REST call by using expect(...).
src/console/ci/qbittorrent_e2e/tracker/client.rs	Propagates REST API client errors with ? in E2E runner wrapper.
src/bin/http_health_check.rs	Removes redundant_else by flattening the non-success branch.
packages/rest-api-client/src/v1/client.rs	Changes ApiHttpClient public methods + free get to return Result and adjusts internal wiring.
packages/axum-rest-api-server/tests/server/v1/contract/context/whitelist.rs	Updates contract tests to unwrap the new Result<Response, ClientError> return values.
packages/axum-rest-api-server/tests/server/v1/contract/context/torrent.rs	Updates contract tests to unwrap the new Result<Response, ClientError> return values.
packages/axum-rest-api-server/tests/server/v1/contract/context/stats.rs	Updates contract tests to unwrap the new Result<Response, ClientError> return values.
packages/axum-rest-api-server/tests/server/v1/contract/context/health_check.rs	Adjusts to get(...) -> Result by unwrapping in the contract test.
packages/axum-rest-api-server/tests/server/v1/contract/context/auth_key.rs	Updates contract tests to unwrap the new Result<Response, ClientError> return values.
packages/axum-rest-api-server/tests/server/v1/contract/authentication.rs	Updates contract tests to unwrap the new Result<Response, ClientError> return values.
docs/issues/open/1969-1938-si-8-eliminate-unwraps-from-rest-api-client.md	Updates issue spec status/progress and documents the two-phase caller strategy.

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[josecelano]

ACK bb0e3d2