[REQ]RAR: Support for Dictionary Configuration

### Is your feature request related to a problem? Please describe
Keka w/ rar does not offer configuration for dictionary sizes.
I process 32-bit float wav files frequently.
A 1GB dictionary could provide about an additional 10% improvement in compression rates(~74%@ def. -> ~65%) for these files.
And rar cli does provide a dictionary config flag.

### Describe the solution you'd like
Let Keka support dictionary configs, like WinRAR does.

### Describe alternatives you've considered
Use as-is. Default RAR5 settings is already superior than 7z and zstd for 32-bit floats.
Using the rar command line. Not quite convenient though.

### Additional context
Add any other context or screenshots about the feature request here.