Remove dependency on XCTest

[sebsto]

Remove dependency on XCTest

Motivation:

As 6.1 does not include XCTest anymore, finish the migration to Swift testing

Modifications:

Replace XCTest by Swift Testing in two files

Result:

swift test works on 6.1.2

[Copilot]

Pull Request Overview

This pull request migrates the testing framework from XCTest to a new Testing package, removing the dependency on XCTest and updating test syntax across multiple files. Key modifications include replacing XCTest assertions with #expect statements, transforming test classes into structs with @test annotations, and updating logging levels in the mock server and client tests.

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
scripts/check-format.sh	Added script to run swift-format on changed files
scripts/check-format-linux.sh	Added Linux-compatible format checking script
Tests/AWSLambdaRuntimeTests/UtilsTest.swift	Updated test suite from XCTest to Testing syntax
Tests/AWSLambdaRuntimeTests/MockLambdaServer.swift	Changed logging levels from info to trace
Tests/AWSLambdaRuntimeTests/LambdaRuntimeClientTests.swift	Commented out logger configuration for trace logging
Tests/AWSLambdaRuntimeTests/ControlPlaneRequestEncoderTests.swift	Refactored test setup and assertions to new syntax

Comments suppressed due to low confidence (1)

Tests/AWSLambdaRuntimeTests/UtilsTest.swift:25

• Double-check that using a struct for the test suite is supported and intended in the new Testing framework, as some frameworks traditionally expect a class.

struct UtilsTest {