feat: split ProcessLauncher by platform, add testingFramework, infinite loop filter and SPM timeout

[ericodx]

Summary

• Launcher separation: Split generic ProcessLauncher into XcodeProcessLauncher (v1.0.0 behavior, no child kill) and SPMProcessLauncher (aggressive child cleanup via kill(-pid, SIGKILL) + killEscapedChildren). Selection at composition root by ProjectType.
• Simulator slot fix: Restore pool.release(slot) before ResultParser.parse() in TestExecutionStage and IncompatibleMutantExecutor.
• Testing framework config: Add testingFramework option (xctest | swift-testing). XCTest + Xcode forces concurrency=1 to prevent parallel simulator interference.
• Auto-detection: init command detects framework by scanning test file imports (import XCTest vs import Testing).
• SPM timeout: Split default timeout by platform — 120s for Xcode, 30s for SPM — to limit CPU waste from infinite loops.
• Infinite loop prevention: Add InfiniteLoopFilter that skips ArithmeticOperatorReplacement and RemoveSideEffects mutations inside while/repeat-while loop bodies. Follows the existing SuppressionFilter pattern.
• Debug cleanup: Remove all [xmr] debug prints from execution stages.

Type of Change

• feat: A new feature has been added.
• fix: A bug has been fixed.
• refactor: A code change that neither fixes a bug nor adds a feature.
• test: Addition or correction of tests.

Invariants Checklist

• Original project is never modified — all mutations happen inside an isolated sandbox
• xcodebuild build-for-testing runs exactly once for all schematizable mutants
• No mutant results are lost or duplicated
• Mutant positions (file, line, column) are accurate in all reported results
• A cancelled task never leaves a simulator slot permanently acquired from the pool
• schematizedContent never contains the __swiftMutationTestingID global declaration
• Swift 6 Strict Concurrency compatible
• Pipeline stages remain stateless pure transformations

Pipeline Impact

Which stages are affected?

• SandboxFactory
• BuildStage
• SimulatorPool
• TestExecutionStage
• IncompatibleMutantExecutor
• PerFileBuildFallback
• CacheStore
• Reporters (Text / JSON / HTML / Sonar)
• CLI / Configuration
• Models / RunnerInput contract
• None

Testing

• Unit tests added or updated
• Tests use mock ProcessLaunching — no real xcodebuild, xcrun simctl, or xcresulttool
• Tests use FileHelpers for any filesystem interaction (temp directories only)
• Snapshot tests added or updated (if reporter output format changed)
• Integration tests added or updated and tagged separately (if pipeline or CLI behavior changed)
• All tests pass locally (swift test)