prompt: tell the agent to leave the measurement setup alone

[ArjunS07]

Purpose

Every Codex patch for bottleneck#309 was rejected because it fixed a bug in an ASV benchmark file. The prompt did not say that these files are off limits. This change tells the agent that these files are restored before measuring (datasmith#59), so edits there are thrown away.

How it works

final.md.j2 renders instruction.md for each task. One line is added to Operating Principles, after "Correctness first":

* **Leave the measurement setup alone**: the ASV benchmark files, `asv.conf*`, `conftest.py` and `.github/` are restored to their original state before your change is measured, so edits there are thrown away. Speed up the library code instead.

Changes

File	Effect	Before
src/datasmith/github/templates/final.md.j2	The prompt names the files that are restored before measuring	The prompt did not mention them

Verification

• pytest tests -k "render or template or prompt" --ignore=tests/docker: 67 passed.

Notes

• Only newly rendered tasks get the line. Rendered tasks keep their instruction.md until they are rendered again or edited.

[atharvas]

Looks good to me.