feat: use RNG instead of chain ID for ERC20 decimals in tests

[DeVikingMark]

Problem

All ERC20 tokens on the same chain have identical decimals (determined by chain ID), limiting test scenarios.

Solution

• Replace provider.get_chain_id().await? % 2 == 0 with rand::random::<bool>()
• Add tests to validate random decimal generation

Changes

• Modified: tests/e2e/environment.rs
  • Updated deploy_erc20() to use RNG for decimal selection
  • Added test cases for decimal randomness validation

Fixes #1345