docs(examples): add benchSDK example benchmarks - #308

Summary

Adds a self-contained benchmarks/examples/ directory with runnable .bench.ts files that demonstrate core @benchsdk/runner patterns without requiring real provider credentials. Each example uses a tiny NoopParticipant helper that simulates create/run/destroy so the files can be exercised against any benchmarks-platform endpoint.

What's added

• benchmarks/examples/participants.ts — mock provider factory implementing BaseParticipant with createCompute().sandbox.create().
• 00-hello-world.bench.ts — single participant, step / measure / log basics.
• 01-multiple-providers.bench.ts — same task against multiple providers, --provider filtering.
• 02-phases.bench.ts — ordered phases with ctx.phase and per-phase iteration counts.
• 03-round-robin.bench.ts — groupBy: 'round' interleaving.
• 04-shapes.bench.ts — named shapes variants selected via --shape.
• benchmarks/examples/README.md — build/run instructions and expected CLI output.
• tsconfig.json — includes benchmarks/examples/**/*.ts so pnpm typecheck covers the new files.

Running an example

pnpm -r --filter "./packages/**" build
bench run benchmarks/examples/00-hello-world.bench.ts --iterations 3

All examples passed pnpm typecheck.

Link to Devin session: https://app.devin.ai/sessions/770c96fe577f4323ae5d7f8ca8b785dc
Requested by: @dtice25