[HAL] Preserve tensor import effects when folding (#24364)

HAL tensor imports carry optional wait fences and consume markers that
are part of the availability and ownership contract for the imported
tensor. Folding through an import/export pair erased that contract,
allowing an async wrapper that returns an imported buffer view unchanged
to discard the wait fence and signal its output fence immediately.

Keep the fold only for imports with no sequencing or ownership effects.
Imports with wait_fence, consume, or byte offsets remain explicit so
later conversion can materialize the required timepoint await or
ownership transfer instead of reducing the wrapper to an immediate
host-side fence signal.

Add canonicalization coverage for both import-to-export and
export-to-import pairs so the plain effect-free fold remains available
while sequenced imports are preserved.

Found while triaging #24324.