Add LDBC benchmarks

[jakewins]

Rust has a built in benchmark framework that seems like a good place to start?

One suggested approach would be something like:

• Get a hold of the LDBC CSV files for some reasonable scale factor (ie something that we can check into the repo)
• Convert those CSV files to gram and gzip it
• Add support for reading gzipped gram files
• Write a few benchmarks that import the gzipped gram file and runs some subset of the LDBC workload