add (Rust) simd-json and rebar to mimalloc-bench

[zooko]

Hi folks! Thanks so much for maintaining mimalloc-bench. In developing my smalloc memory allocator, I've benefited from mimalloc-bench. Also I found two other projects from the Rust ecosystem that have benchmarks that I was able to adapt to use mimalloc, snmalloc, rpmalloc, and jemalloc, using Rust wrappers for each of those. Maybe you'd like to add this into mimalloc-bench (whether with the Rust wrappers or with mimalloc-bench's current LD_PRELOAD technique). They are https://github.com/simd-lite/simd-json and https://github.com/BurntSushi/rebar .

Here you can find my forks of those repos to run their benchmarks with various memory allocators: https://github.com/zooko/simd-json and https://github.com/zooko/rebar . And here are the instructions for how to run the benchmarks: https://github.com/zooko/smalloc/blob/main/bench/README.md#benchmarking-user-code-with-different-allocators

Here are some benchmark results generated with this process:

using the simd-json codebase:

test                                                                            default                jemalloc                snmalloc                mimalloc                rpmalloc                 smalloc
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
...
NORMALIZED (100s baseline work)                                      2100.0 s  (      )      2096.4 s  (      )      1944.6 s  (      )      1778.1 s  (      )      1756.2 s  (      )      1711.9 s  (      )
RELATIVE TO BASELINE                                                           ( +0.0%)                ( -0.2%)                ( -7.4%)                (-15.3%)                (-16.4%)                (-18.5%)

using the rebar codebase:

Engine               Version  Geometric mean of speed ratios  Benchmark count
------               -------  ------------------------------  ---------------
rust/regex-snmalloc  1.12.2   1.01                            52
rust/regex-rpmalloc  1.12.2   1.02                            52
rust/regex-smalloc   1.12.2   1.03                            52
rust/regex-mimalloc  1.12.2   1.03                            52
rust/regex-jemalloc  1.12.2   1.07                            52
rust/regex           1.12.2   1.09                            52