Fixes issue #28 where bunv incorrectly reports "Failed to install Bun" despite successful installation.

Problem

The installation process was checking exit codes incorrectly in src/vm.zig line 220:

if (installProcess.term.Exited == 0) {
    std.debug.print("Failed to install Bun:\n\nSTDERR:\n{s}\n\nSTDOUT:\n{s}\n", .{ installProcess.stderr, installProcess.stdout });
    std.process.exit(1);
}

In Unix/Linux systems:

• Exit code 0 means SUCCESS
• Exit code != 0 means FAILURE

The condition was backwards, treating successful installations (exit code 0) as failures.

Example of the Bug

❯ bun --version
Bun v1.2.18 is not installed. Do you want to install it? [y/N] y
Installing...
Failed to install Bun:

STDOUT:
-e bun was installed successfully to ~/.bunv/versions/1.2.18/bin/bun 
Run 'bun --help' to get started

Solution

Changed the condition from == 0 to != 0 to correctly detect failures:

if (installProcess.term.Exited != 0) {
    std.debug.print("Failed to install Bun:\n\nSTDERR:\n{s}\n\nSTDOUT:\n{s}\n", .{ installProcess.stderr, installProcess.stdout });
    std.process.exit(1);
}

Now:

• ✅ Successful installation (exit code 0) → Shows success message
• ✅ Failed installation (exit code ≠ 0) → Shows error message and exits

Changes

• 1 character change in src/vm.zig line 220: == → !=
• Makes the code consistent with other exit code checks in the same file (line 186)

Closes #28