fix: let an interrupt stop the parse, release striff-lib 4.3.3

[Zir0-93]

Closes #73.

Releases striff-lib 4.3.3.

Problem

StriffOperation parsed the base and head revisions with CompletableFuture.supplyAsync on the common pool and waited with join(). join() ignores interrupts, and the threads doing the parsing were never the thread a caller interrupts. Clarpse's cooperative cancellation checks watch the thread they run on, so they never fired: a caller enforcing a time budget with Thread.interrupt() could not stop a parse. The parse ran to completion, and the interrupt was only noticed afterwards at the CodeDiff merge checkpoint.

Change

• New package-private ParallelParse runs the two parses on a two-thread pool it owns. The caller waits interruptibly; an interrupt cancels both parses (interrupting their threads, where Clarpse's checks see it) and the call throws CancellationException with the interrupt flag re-asserted, matching the existing checkpoints in CodeDiff and ExtractedRelationships.
• No parse outlives the call: whatever ends the wait, both threads are stopped and awaited before it returns. A parse that ignores its interrupt still runs to completion, as before; it is never reported as stopped when it is not.
• Results are taken in completion order, so one failed parse ends the wait and stops the other instead of leaving it running in the background.
• Behaviour note: a CompileException from a parse now reaches the caller as itself. It was previously wrapped in a RuntimeException by the lambda, which defeated the unwrapping joinCompileResult intended.
• README gains a short Cancellation section; StriffOperation's full-pipeline constructor documents it.
• Version 4.3.2 → 4.3.3.

Verification

• mvn clean package -B on JDK 17 and JDK 21: 213 tests, 0 failures; Checkstyle and PMD clean. PMD's CloseResource is suppressed on ParallelParse.run: ExecutorService is AutoCloseable only from Java 19, so try-with-resources is unavailable at the Java 17 baseline, and the pool is shut down and awaited in a finally.
• ParallelParseTest (4 tests): the interrupt reaches both parse threads and the call returns only after both parses have ended; a failed parse stops the other without waiting for it; ordinary results are returned by revision; an interrupted StriffOperation throws CancellationException. Thread-count checks allow a pool thread a bounded moment to finish exiting, since a pool reports termination from inside its last worker; the parses having ended is pinned by latches. 10 repeated runs on JDK 21 passed.
• Red check: with ParallelParse temporarily reverted to the old supplyAsync + join() wait, two of the new tests fail for the expected reasons: the interrupt test ("the call must return once its thread is interrupted") and the failed-parse test (times out waiting behind the blocked parse).

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