Shared benchmark infrastructure for vibesql benchmarks

This crate provides common benchmark code used by both vibesql-executor and vibesql-server benchmark suites:

• TPC-C: OLTP transaction processing benchmark
• TPC-H: Decision support (OLAP) benchmark
• TPC-DS: Decision support benchmark with complex queries
• TPC-E: Financial trading benchmark
• Sysbench: MySQL-compatible micro-benchmarks
• Harness: Timing and statistics infrastructure

Phase 1 - Data Generators and Types

This initial version provides portable data generators and type definitions that don't depend on any vibesql crates. Engine-specific schema loading and transaction execution code remains in each benchmark crate.

Usage

Add as a dev-dependency in your crate's Cargo.toml:

[dev-dependencies]
vibesql-bench-common = { path = "../vibesql-bench-common" }