fix(rustic-babel-build-sentinel): align behaviour with other lang

[ed9w2in6]

In an org file, the src block's code should be interpreted, OR the binary compiled from it SHOULD execute with PWD as default-directory of the org file.

Summary of changes:

1. save the original default-directory then later restores it.
2. supply --manifest-path option to cargo run to execute the target Cargo.toml binary compiled from the src block.

For reference:
Try to execute a C++, C, js (node), python block.
In particular, see implementation of org-babel-C-execute or org-babel-python-evaluate-external-process.
May be we can re-write like them in the future.

fixes: #509

[ed9w2in6]

The 2 code block should yield identical outputs when executed in a src block of a org file.

Rust

use std::env;
use std::fs;
use std::io;

fn main() -> io::Result<()> {
    for f in fs::read_dir(".")? {
        let fpath = f?.path();
        let fname = fpath.to_str().expect("Path should convert to str");
        println!("{fname}");
    }
    Ok(())
}

C++

#include <string.h>
#include <dirent.h>
#include <stdio.h>

using namespace std;

int main() {
DIR *dir;
struct dirent *dp;

dir = opendir(".");
while ((dp = readdir(dir)) != NULL) {
  // printf("debug: %s\n", dp->d_name);
  if ( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") ) {
    // do nothing (straight logic)
  } else {
    printf("./%s\n", dp->d_name);
  }
}
closedir(dir);
return 0;
return 0;
}

Here is a sample org file for your reference.

Sample Org File

#+TITLE:Loop Do Nothing
* Components
** foobar
   #+begin_src rustic :results output scalar :eval yes :main no
use std::env;
use std::fs;
use std::io;

fn main() -> io::Result<()> {
    for f in fs::read_dir(".")? {
        let fpath = f?.path();
        let fname = fpath.to_str().expect("Path should convert to str");
        println!("{fname}");
    }
    Ok(())
}
   #+end_src

#+begin_src C++ :results scalar :eval yes :includes <string.h> <dirent.h> <stdio.h> :namespaces std
DIR *dir;
struct dirent *dp;

dir = opendir(".");
while ((dp = readdir(dir)) != NULL) {
  // printf("debug: %s\n", dp->d_name);
  if ( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") ) {
    // do nothing (straight logic)
  } else {
    printf("./%s\n", dp->d_name);
  }
}
closedir(dir);
return 0;
#+end_src