fix(artillery): align init helpers, state cache, and docs

[Ansonhkg]

WHAT

• resolve Artillery init so it consumes exported helpers and writes state containing bigint values
• add docs for Artillery

HOW TO RUN

• pnpm nx run artillery:init
• (optional) pnpm nx run artillery:balance-status
• pnpm nx run artillery:run:pkp-sign

[Copilot]

Pull Request Overview

This PR consolidates import paths for Artillery utilities and adds BigInt serialization support to the state manager, along with comprehensive documentation for Artillery load testing.

• Simplified imports from @lit-protocol/e2e package by using the package's public API instead of deep imports
• Added BigInt serialization support in StateManager to prevent JSON serialization errors
• Added Artillery load testing documentation with setup, initialization, and workload execution instructions

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
packages/artillery/src/init.ts	Consolidated imports to use @lit-protocol/e2e package exports instead of deep paths
packages/artillery/src/StateManager.ts	Added stringify helper function with BigInt replacer to handle BigInt JSON serialization
README.md	Added comprehensive Artillery load testing documentation including setup, initialization, and workload scenarios

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[Copilot]

The stringify function lacks documentation explaining its purpose. Add a JSDoc comment explaining that it serializes objects to JSON with BigInt support, as BigInt values cannot be directly serialized by JSON.stringify.