viz: keep program UOp in data

[Qazalin]

it's recomputable but expensive with the for loop. Since rewrite names can repeat, the data structure needs to stay as a list.

time extra/viz/cli.py -p -s "AMD" on llama went from 20s to 10s, same impact on viz web startup.

[github-actions]

Changes

Name                     Lines    Diff    Tokens/Line    Diff
---------------------  -------  ------  -------------  ------
tinygrad/viz/serve.py      654      +0           17.2    -0.0


total lines changes: 0