COR-173 - Add IMAP interrupt command support

[dbezverkhnii]

Note

Medium Risk
Changes threaded operation-queue state and cancels live IMAP streams; misuse could drop connections or cause extra reconnects, though the API is scoped to the running operation and documented as abandon-only.

Overview
Adds a way to abort the IMAP command already running on an operation’s connection so blocked socket reads return immediately instead of waiting for the session timeout—mainly so teardown (e.g. disconnect queued behind a stuck command) can proceed without sitting behind a hung read.

The stack is wired from OperationQueue (tracks mRunningOperation, interruptRunningOperation under the queue lock) through IMAPOperation::interrupt() / interruptCurrentCommand(), IMAPAsyncConnection, and IMAPSession::interruptCurrentCommand() (mailstream_cancel while the session lock is held). The call is synchronous and bypasses the operation queue so it can unblock the operation currently in main(). It only affects the operation that is actually running; queued operations get false. Docs stress teardown-only: the stream stays cancelled and the connection must be rebuilt on next use—unlike cancel(), which only sets a flag before main().

interruptCurrentCommand is exposed on the C bridge and Swift IMAPBaseOperation. Darwin-only IMAPInterruptCurrentCommandTests use a silent TCP listener to simulate a blocked connect and assert interrupt behavior vs queued operations.

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