Add offloading options to vmnet-run

[nirs]

Add --enable-tso and --enable-checksum-offload options to vmnet-run, passed through to vmnet-helper. These options were previously only available when running vmnet-helper directly.

Since macOS 26.2 offloading works well and can significantly improve network performance. For example, with krunkit on M2 Max, host network throughput is 3-5x faster with offloading (~30 Gbits/s tx, ~47 Gbits/s rx vs ~7-10 Gbits/s without offloading).

Note that offloading does not work for all use cases. For example, accessing the VM from pod network does not work with offloading enabled (see #179).

Example run:

% ./example server --driver krunkit --cpus 4 --connection=runner --enable-offloading
[   0.052] INFO Creating cloud-init iso '/Users/nir/.vmnet-helper/vms/server/cidata.iso'
[   0.059] INFO Starting 'krunkit' virtual machine 'server' with mac address '76:d4:d3:83:fc:14'
[   6.079] INFO Virtual machine IP address: 192.168.105.2

% iperf3 -c server-vmnet-helper.local
...
[ ID] Interval           Transfer     Bitrate
[  7]   0.00-10.01  sec  43.2 GBytes  37.1 Gbits/sec                  sender
[  7]   0.00-10.01  sec  43.2 GBytes  37.1 Gbits/sec                  receiver

% iperf3 -c server-vmnet-helper.local -R
...
[ ID] Interval           Transfer     Bitrate         Retr
[  7]   0.00-10.00  sec  52.7 GBytes  45.3 Gbits/sec    0            sender
[  7]   0.00-10.00  sec  52.7 GBytes  45.3 Gbits/sec                  receiver

Fixes #177