Add test coverage for detected commands running in sandbox

[hanabel1]

• adds unit tests for DetectCommands covering every toolchain. The function didn't have any tests before.
• adds TestDetectPackageManager covering each lockfile type and monorepo subdirectory detection
• Adds TestDetectCommandsAndRunRemoteSSH which wires detected commands through runRemote into the fake ssh server, making sure that a Go project's go test ./..., a node project's npm test, and a Taskfile project's task test are correctly formatted and sent to the sandbox
• Add's sandbox image smoke tests verifying the tools chunk relies on are present in Dockerfile.sandbox.

[danmux]

Reviewed — approving.