fix: use pointer receivers for composeService methods with sync.Once fields

Moving runtimeVersionCache from a package-level var to instance fields on
composeService caused copylocks violations in methods using value receivers,
since sync.Once contains sync.noCopy. Switch the 4 affected methods to
pointer receivers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Guillaume Lours <glours@users.noreply.github.com>