fix: resolve CheckedContinuation deadlock in NetworkTransport on actor dealloc (Swift 6.3)

[doozMen]

Summary

Fixes #214 — CheckedContinuation never resumed in NetworkTransport send()/sendHeartbeat()/receiveData() when the actor deallocates during an in-flight NWConnection operation. This causes a permanent deadlock.

Discovered via Swift 6.3 strict concurrency checking, but the bug exists in all Swift versions using this transport.

Changes

NetworkTransport.swift

• send(): Changed completion closure capture from [weak self] to [weak self, continuation]. Added continuation.resume(throwing:) in the guard let self else branch.
• sendHeartbeat(): Same fix — completion closure now captures continuation directly and resumes with error on dealloc.
• receiveData(): Changed from implicit strong self capture to explicit [weak self, continuation] for consistency. All four branches already resumed the continuation; this hardens the capture semantics.

Client.swift

• withBatch(): Fixed early-return path to return result instead of implicit void (was broken for non-Void generic T).

ClientTests.swift

• Added testBatchRequestEmptyNonVoid() — verifies withBatch returns the closure result when no requests are added (non-Void path).

Housekeeping

• Removed accidentally committed .claude/settings.local.json and .swift-version
• Added both to .gitignore

The Pattern

// BEFORE (deadlock on dealloc):
completion: .contentProcessed { [weak self] error in
    guard let self else { return }  // ← continuation leaked!

// AFTER (safe):
completion: .contentProcessed { [weak self, continuation] error in
    guard let self else {
        continuation.resume(throwing: MCPError.internalError("Transport deallocated"))
        return
    }

CheckedContinuation is Sendable — safe to capture directly alongside [weak self]. This decouples the continuation's lifetime from the actor, guaranteeing resumption even on dealloc.

Testing

• swift build — clean
• swift test --filter testBatchRequestEmpty — 2 tests pass
• Audited sendHeartbeat() — already correct in outer guard, fixed inner completion
• Verified Logger is nonisolated let + Sendable — safe to access from completion closures

[movetz]

Fixed in #203 and available in the latest v0.12 release. Please check.