devel/py-inotify-simple: use native inotify on FreeBSD 15+

FreeBSD 15 (OSVERSION >= 1500051) provides native inotify in libc.
Use native libc on FreeBSD 15+ and Linux; fall back to libinotify on
older FreeBSD releases which require the kqueue-based emulation.

Remove unconditional LIB_DEPENDS on libinotify and make it conditional
using the bsd.port.pre.mk/bsd.port.post.mk split.

PR: ports/294447
Approved by: maintainer timeout