use actual macos memory usage from libproc pid_rusage

[forivall]

I'd also like to add a column to show the raw bytes from ri_phys_footprint, but i'm not sure if i should create a new column or which existing column to use (I'm thinking of making a new VmTotal or VmPss column, which could be calculated appropriately for other operating systems)

[dalance]

I agree to add VmTotal column.

I update MSRV to fix MSRV CI failure. So could you fix other CI failures and add VmTotal column to README.md?