lookup_lib returns all the benchmarks from the specified library
val add_bench : name:string -> code:string -> filename:string -> type_conv_path:string -> line:int -> startpos:int -> endpos:int ->Entry.test_spec-> unit
add_bench registers benchmarks with the global hashtable maintained in ppx_bench_lib. This is meant to be called by the code generated for the BENCH and BENCH_INDEXED macros