Use launchctl load -w on macOS

[cole-h]

Usage: launchctl load <service-path, service-path2, ...>
        -w      If the service is disabled, it will be enabled. In previous
                versions of launchd, being disabled meant that a service was
                not loaded. Now, services are always loaded. If a service is
                disabled, launchd does not advertise its service endpoints
                (sockets, Mach ports, etc.).

Description

Attempts a simple fix for #295.

Checklist

• Formatted with cargo fmt
• Built with nix build
• Ran flake checks with nix flake check
• Added or updated relevant tests (leave unchecked if not applicable)
• Added or updated relevant documentation (leave unchecked if not applicable)
• Linked to related issues (leave unchecked if not applicable)

Validating with install.determinate.systems

If a maintainer has added the upload to s3 label to this PR, it will become available for installation via install.determinate.systems:

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix/pr/$PR_NUMBER | sh -s -- install