Port IPC::SysV (low priority)

[fglock]

Summary

Port IPC::SysV to PerlOnJava using Java FFM/native access on Unix platforms.

This is a low-priority ecosystem-enablement task. The current targeted
MetaCPAN lookup found 14 released runtime dependants, including
IPC::Pleather, IPC::Transit, IPC-Shm-Simple, SysV-SharedMem, and
Proc-Swarm; 2 were recent dependants. Recheck this count before prioritizing
implementation, and increase priority if the dependant population grows.

Scope

• Provide the IPC::SysV constants and ftok behavior.
• Implement System V semaphores: semget, semop, semctl, and the
  IPC::Semaphore support they require.
• Implement shared memory: shmget, shmat, shmdt, shmctl, memread,
  and memwrite.
• Implement message queues: msgget, msgsnd, msgrcv, and msgctl.
• Preserve Perl-visible return values, errno/error behavior, cleanup, and
  concurrency semantics.
• Define platform behavior explicitly: native Unix support first; Windows
  should either use a real compatible implementation or fail clearly if SysV
  IPC is unavailable.

Existing groundwork

The bytecode backend already has operation slots and compiler/interpreter
scaffolding for semaphore, message-queue, and shared-memory operations, but
the handlers currently throw UnsupportedOperationException.

Acceptance criteria

• Focused project-owned tests cover constants, semaphore operations, shared
  memory, message queues, errors, cleanup, and cross-process visibility where
  supported.
• Tests pass on both JVM and interpreter backends where applicable.
• At least one dependent module is validated after the port.
• Documentation records supported platforms and limitations.

Related: #1144 (pseudofork support may remain a separate requirement for
modules that depend on fork).