feat: add benchmark results artifact (JSON) #3185
Description
Add a machine-readable JSON file to the repo containing benchmark results from the 5-test matrix. Structure is TBD — will be defined after the first round of test PRs land (TestSequencerOverhead, TestDeFiSimulation, TestStatePressure).
This artifact serves as a regression baseline for future runs and a data source for charts/reports.
Related: #2288