add mobench support to ProveKit main

[dcbuild3r]

Summary

• add main-based mobench fixtures for passport, OPRF, and P-256 bigcurve
• run BrowserStack smoke profile on iPhone 7 and Vivo Y21 device profiles
• harden sticky comment reporting and low-end BrowserStack retry/timeout handling

CI note

The authoritative draft PR lives in worldfnd/provekit. CI validation runs are dispatched in dcbuild3r/provekit as a mirror to test whether the mobile fixtures work.

Current device status

• Vivo Y21 uses BrowserStack device spec Vivo Y21-11.0.
• BrowserStack inventory only exposes iPhone 7 as iPhone 7-10; the branch keeps that real inventory target. Xcode 16/mobench XCUITest artifacts currently upload with a minimum OS above iOS 10, so exact iPhone 7 execution is blocked at BrowserStack scheduling until the runner/toolchain supports that OS or BrowserStack exposes a newer iPhone 7 image.

Validation

• cargo check -p bench-mobile
• cargo test -p bench-mobile --test examples_smoke
• cargo test -p bench-mobile --test passport_smoke
• actionlint .github/workflows/mobile-bench-reusable.yml .github/workflows/mobile-bench.yml
• git diff --check