Run subprocesses and access process utilities:

```vary
import process

let result = process.run(["ls", "-la"], cwd="/tmp")
print(result.stdout())

let out = process.cmd("echo").arg("hello").capture()

let cwd = process.getcwd()
let args = process.argv()
```

| **Function** | **Returns** | **Description** |
|----------|---------|-------------|
| `process.run(args, cwd?, env?)` | `ProcessResult` | Run a subprocess |
| `process.cmd(program)` | `Command` | Create a fluent command builder |
| `process.getcwd()` | `Str` | Return current working directory |
| `process.realpath(p)` | `Str` | Return canonical path, resolving symlinks |
| `process.tempdir()` | `Str` | Return system temporary directory |
| `process.exit(code)` | `None` | Exit with status code |
| `process.argv()` | `List[Str]` | Return command-line arguments |

`ProcessResult` methods:

| **Method** | **Returns** | **Description** |
|--------|---------|-------------|
| `.exit_code()` | `Int` | Process exit code |
| `.stdout()` | `Str` | Captured standard output |
| `.stderr()` | `Str` | Captured standard error |
| `.ok()` | `Bool` | True if exit code is 0 |
| `.require_ok()` | `ProcessResult` | Returns self or throws if exit code is non-zero |

`Command` builder methods:

| **Method** | **Returns** | **Description** |
|--------|---------|-------------|
| `.arg(value)` | `Command` | Append a single argument |
| `.args(values)` | `Command` | Append multiple arguments |
| `.with_cwd(path)` | `Command` | Set working directory |
| `.with_env(name, value)` | `Command` | Set environment variable |
| `.run()` | `ProcessResult` | Execute and return result |
| `.check()` | `ProcessResult` | Execute and throw if non-zero exit |
| `.capture()` | `Str` | Execute and return stdout (throws if non-zero exit) |