perf: build-time leads found while profiling Window #116

Moved from chunkzero/window#58, which tracks the Window side. These are the rpp leads, roughly by expected payoff. None has been measured in isolation yet.

• Generator re-evaluation on edit builds. The generator evaluates the plugin's bundle a second time on edit builds. Skipping the redundant pass should cut edit-build resolve time.
• Byte-list fast path in rpp-wasm. list<u8> results are lifted as one wasmtime Val per byte. A typed or bytes path would cut the conversion time and the hostcall fuel spent. fix(wasm): lift hostcall fuel limit for large component outputs #111 raised the fuel limit but left this conversion as it was. It mainly affects PNG outputs.
• Per-file squash optimize cache. With png: fast or max, an edit build re-optimizes every PNG. Caching optimized output by content hash would make edit builds scale with the files that changed.
• Watch-mode rebuilds. Re-measure the above in a dev session, where process startup is not paid and warm in-process state could skip more work.

Reference numbers from Window's just bench on 0.1.0-nightly.20261008133812 (median wall ms, JSX): 1x cold 118, 1x edit 107, 10x cold 339, 10x edit 303, 10x no-op 42.