feat: add configurable EL_PREMINE_COUNT and EL_PREMINE_BALANCE for dynamic premine account generation

[ashrhmn]

Summary

• Add EL_PREMINE_COUNT environment variable to control number of premine accounts (default: 21)
• Add EL_PREMINE_BALANCE environment variable to set balance per account (default: 1000000000ETH)
• Dynamically generate premine entries in genesis generation script
• Handle EL_PREMINE_COUNT=0 to disable auto-funded accounts entirely
• Simplify genesis-config.yaml by removing hardcoded premine entries