Update the .envrc for probe_frontend to automatically run make on
libprobe, as well as export the __PROBE_LIB environment variable so that
the frontend can find the libprobe.so

Co-authored-by: Sam Grayson <sam@samgrayson.me>

Removes a lot of details that are usually abstracted by libraries when
printing for humans. In contrast with some of the code review comments I
left mtime and errno field because I feel those are useful for human
readers; even if all a human is likley to do with errno is "was it
zero?"

This commit addresses serveral points raised durring the last
code-review (and a few that weren't):

- Restructured arena.rs to read top-down.
- Refactored child process code to use std::process instead of
subprocess crate.
- Cleaned up arena pointer resolition to use less unsafe code.
- [INFO] Better log messages.

Co-authored-by: Sam Grayson <sam@samgrayson.me>

the structs now get converted to camel case at the rust level instead of
the python level meaning python doesn't have to do any type name
translation. Also strips out redundant field prefixes from the rust
structs (which also solves the issue for python).

building the probe cli with `cargo build` inside the devShell will still
produce a dynamically linked binary, but building with `nix build
.#probe-cli` should produce a statically linked binary