[treeform]

Scaled UI frames allocated a new vertex buffer, and unchanged input frames allocated a closure environment while checking callback identities. Reuse the context's scaled vertex storage and create input wrappers only when a callback actually changes.

Validation:

• Added a regression asserting zero allocations across 100 unchanged input frames, and enabled it in CI with -d:nimTypeNames.
• Nim checks and input, layout, layout regression, clipping, atlas, and textbox tests.
• Native and WASM GotA rendering checked; its warmed render capture has no recurring allocations with these fixes and the accompanying renderer cleanup.