fix(library/blast/blast): avoid unnecessary calls to set_local_instances
fix(library/blast/blast): avoid unnecessary calls to set_local_instances

This was producing a performance problem since the cache is invalidated/flushed
whenever we call this method.

javra/lean,fpvandoorn/lean,fgdorais/lean,fpvandoorn/lean2,soonhokong/lean-windows,rlewis1988/lean,UlrikBuchholtz/lean,leanprover-community/lean,UlrikBuchholtz/lean,leanprover/lean,Kha/lean,leanprover/lean,leanprover-community/lean,johoelzl/lean,avigad/lean,soonhokong/lean,rlewis1988/lean,javra/lean,UlrikBuchholtz/lean,leanprover/lean,levnach/lean,fpvandoorn/lean2,fgdorais/lean,rlewis1988/lean,leodemoura/lean,johoelzl/lean,fpvandoorn/lean,avigad/lean,leanprover/lean,avigad/lean,digama0/lean,digama0/lean,leanprover/lean,levnach/lean,leanprover-community/lean,soonhokong/lean-windows,leodemoura/lean,digama0/lean,leodemoura/lean,Kha/lean,levnach/lean,johoelzl/lean,leanprover-community/lean,dselsam/lean,Kha/lean,UlrikBuchholtz/lean,javra/lean,soonhokong/lean-osx,fpvandoorn/lean,dselsam/lean,fgdorais/lean,rlewis1988/lean,digama0/lean,Kha/lean,soonhokong/lean-osx,UlrikBuchholtz/lean,fpvandoorn/lean,dselsam/lean,soonhokong/lean-osx,fgdorais/lean,soonhokong/lean-osx,fpvandoorn/lean2,leodemoura/lean,soonhokong/lean-windows,soonhokong/lean,fgdorais/lean,soonhokong/lean-windows,soonhokong/lean,javra/lean,Kha/lean,fpvandoorn/lean,rlewis1988/lean,johoelzl/lean,soonhokong/lean,rlewis1988/lean,dselsam/lean,levnach/lean,dselsam/lean,soonhokong/lean-osx,leanprover-community/lean,dselsam/lean,fgdorais/lean,fpvandoorn/lean2,fpvandoorn/lean,avigad/lean,johoelzl/lean,fpvandoorn/lean2,digama0/lean,javra/lean,Kha/lean,levnach/lean,soonhokong/lean-windows,digama0/lean,leanprover/lean,soonhokong/lean,avigad/lean,leanprover-community/lean,avigad/lean,johoelzl/lean,leodemoura/lean,leodemoura/lean