Reduce allocations in `evaluate!` and `set_eval_nodes!`

[oyamad]

evaluate! and set_eval_nodes! allocate a lot when evaluating on non-interpolation grids. This looks like a worthwhile optimization target.

Current code path

evaluate! currently does:

• res.V, res.X = s_wise_max(...)
• res.resid = res.V - vec(funeval(...))

set_eval_nodes! updates the stored evaluation nodes and then immediately calls evaluate!.

Possible directions

• make evaluate! reuse preallocated V, X, and resid
• add an in-place evaluation path for the residual computation
• reduce temporary arrays created by s_wise_max(...)
• keep API behavior the same while making internals more workspace-oriented

Related to existing discussion in #10.

(AI assisted (ChatGPT Pro 5.4) in drafting this issue)