fix: harden macimed socket server reliability

[tlhc]

• Cache TextInputSources snapshots and refresh after lookup or selection failures
• Serialize daemon command execution for non-thread-safe TextInputSources APIs
• Configure accepted sockets with SO_NOSIGPIPE, SO_RCVTIMEO, and SO_SNDTIMEO
• Retry socket response writes after short writes and EINTR
• Run blocking client I/O on a concurrent DispatchQueue
• Raise the pending-connection backlog from 5 to 64
• Add CI integration tests for source-cache refresh, idle peers, disconnected clients, concurrent requests, and JSON responses

[Copilot]

Pull request overview

This PR hardens the macimed UNIX-domain socket daemon to be more reliable under concurrency, idle/disconnected clients, and transient socket I/O issues, while also improving input-source handling by caching TIS snapshots with refresh-on-failure behavior and adding CI-covered tests.

Changes:

• Introduce an InputSourceCache to cache TISInputSource snapshots and refresh on lookup/selection failures.
• Improve socket server robustness (socket options, concurrent connection handling, serialized command execution for non-thread-safe TIS/TSM APIs, backlog increase, retry short writes/EINTR).
• Add new unit/integration test targets and run swift test in CI.

Reviewed changes

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

Show a summary per file

File	Description
Tests/MacIMEKitTests/IMECacheTests.swift	Adds unit tests validating cache refresh and selection retry behavior.
Tests/MacIMEIntegrationTests/IMEDSocketTests.swift	Adds integration tests for idle/disconnected clients, concurrency, and JSON response validity.
Sources/MacIMEKit/IMED.swift	Hardens daemon socket handling (socket options, queues, write-retry, backlog increase).
Sources/MacIMEKit/IME.swift	Adds InputSourceCache and selection retry/refresh logic for input sources.
Package.swift	Registers new test targets for unit + integration tests.
.github/workflows/test.yml	Runs swift test in CI (and keeps release build + direct CLI sanity check).

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[riodelphino]

@tlhc
Thank you for great PR.
Such a professional work hardening macime is really appreciated.
I will clone it in local and check it.
Please wait a moment.

[riodelphino]

@tlhc
I took a look through the PR.

There are quite a lot of changes, and honestly most of them go beyond my current level of Swift understanding — I had to ask an AI to help me understand the purpose behind each change.

Given that, I'm a bit hesitant about merging this without fully understanding it myself 😅

One thing I wanted to ask:

in d44f8e7 commit, I replaced all DispatchQueue usage with Task/async/await.

This PR reintroduces DispatchQueue in a few places — was there a specific reason for that? My guess is it's because DispatchQueue is needed to handle blocking I/O safely, but I wanted to confirm your reasoning before merging.

[tlhc]

This PR reintroduces DispatchQueue in a few places — was there a specific reason for that? My guess is it's because DispatchQueue is needed to handle blocking I/O safely, but I wanted to confirm your reasoning before merging.

Yes, you are right, Make sure the req is safe to handle