fix: flush stdout after writes for real-time RPC notifications

[zerone0x]

Summary

Fixes #23

Adds synchronize() call after stdout writes to prevent buffering delays in RPC notifications.

Problem

Swift's FileHandle.standardOutput buffers writes by default. Without explicit flushing, RPC notifications accumulate in the buffer (~4-8KB) and are delayed by 3-9 minutes in low-traffic scenarios.

As described in the issue:

• Individual notification messages are small (~200-500 bytes)
• Buffer doesn't fill quickly in low-traffic scenarios
• Results in burst delivery when buffer finally flushes

Solution

Add try? FileHandle.standardOutput.synchronize() after each write in StdoutWriter.writeLine():

static func writeLine(_ line: String) {
  queue.sync {
    FileHandle.standardOutput.write(Data((line + "\n").utf8))
    // Flush immediately to ensure real-time delivery of RPC notifications
    try? FileHandle.standardOutput.synchronize()
  }
}

Testing

This fix ensures imsg rpc watch notifications are delivered immediately, matching the real-time behavior of the underlying FSEvents watcher.

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