Dynamically discover impl types in benchmark HTML

[mokita-j]

• Dynamically discover PVM implementation types (Rust, Ink, Stylus, etc.) from the database instead of hardcoding them in charts, tables, and SQL queries
• Extract dataset definitions into benchmark/datasets.ts to break circular imports
• Defer initEnv() to only when --execute is used — --build, --report, and --html-report no longer require an RPC connection
• Use lazy proxy for env in tools/lib/index.ts with clear error on uninitialized access
• Add initEnv() calls to all CLI playground scripts
• Assign chart colors sequentially from a palette (no collisions) instead of via hash or hardcoded maps
• Fix type errors (SQLite casts, viem hex/bigint types)