EnsureRequirements returns Transformed::yes unconditionally, forcing a full plan rebuild

[zhuqi-lucas]

Describe the bug

EnsureRequirements returns Transformed::yes unconditionally at three places, so transform_up rebuilds every ancestor node and recomputes its PlanProperties even on a pass that changes nothing, and the rule always hands back a fresh Arc.

// physical-optimizer/src/ensure_requirements/mod.rs
plan.transform_up(|p| Ok(Transformed::yes(reorder_join_keys_to_inputs(p)?)))
    .transform_up(|p| Ok(Transformed::yes(replace_with_partial_sort(p)?)))

// physical-optimizer/src/ensure_requirements/enforce_distribution.rs, end of ensure_distribution
Ok(Transformed::yes(optimized_context))

The flag is what decides whether a node is rebuilt:

// common/src/tree_node.rs
if new_children.transformed {
    self.with_new_arc_children(arc_self, new_children)   // rebuild, recompute properties
} else {
    Ok(Transformed::new(self, false, new_children.tnr))  // reuse the original Arc
}

Reporting yes when nothing changed therefore costs a full rebuild of the plan, and removes the caller's ability to tell that nothing happened.

To Reproduce

Run EnsureRequirements on a plan it has already settled and compare the result with Arc::ptr_eq. It is never equal.

Expected behavior

Report what actually happened. A pointer comparison against the input is enough at each of the three sites:

let before = Arc::clone(&p);
let after = reorder_join_keys_to_inputs(p)?;
Ok(if Arc::ptr_eq(&before, &after) { Transformed::no(after) } else { Transformed::yes(after) })

Additional context

Measured on a real 34-node plan through a chain with six enforcement passes. Of 23 calls that left the plan byte-identical, fixing these three sites makes 7 also return the input object, which callers can then detect for free.

The remaining 16 still rebuild, because the distribution and sorting phases inside the rule change the plan and then change it back. That is a separate problem, filed as #25360.

Found while measuring #25355 / #25356, where this is why plans have to be compared by rendered form rather than by pointer.

[zhuqi-lucas]

I have the three-site fix on a branch and measurements for it; happy to open a PR if the direction is welcome.