Uninitialized buffers are disjoint from immutable buffers.
Uninitialized buffers are disjoint from immutable buffers.

Proof by contradiction; the preorders must be identical if the buffers
are non-disjoint. This is limited to inhabited types; if `t` is
uninhabited, the buffer can only contain `None` (never `Some t`),
in which case `initialization_preorder` and `immutable_preorder`
behave identically.

Derived from ImmutableBuffer.buffer_immutable_buffer_disjoint.

FStarLang/FStar,FStarLang/FStar,FStarLang/FStar