feat(bench): add tooling for synthetic native transfer benchmarks (#1…

…2570)

Adds tooling to benchmark native token transfers with the
`benchmark-native-transfer` command. The accounts involved in that
benchmark can be generated with `create-sub-accounts`. Examples of how
to execute both commands are given in the `justfile`. Documentation is
available in `benchmarking_synthetic_workloads.md`.

The tooling is based on Rust and `near-jsonrpc-client`. Having the Rust
toolchain installed should be sufficient to use it.

This PR is rather big. Splitting it up into smaller pieces would result
in parts that don't fully support running a workload. I assume that
wouldn't be favorable.

The code added here is benchmark tooling only which doesn't affect
`neard`, so I it shouldn't be able to break anything in production.

benchmarks/synth-bm/.gitignore

@@ -0,0 +1,3 @@
+.near/
+target/
+user-data/