[feature request] synthesizing multiple hotkeys per instance of skhd

It would be great for skhd to accept multiple `-k` or `-t` options to allow synthesizing keypresses many times per one execution of `skhd`.

Usecase: I'm attempting to make a vim-like mode using skhd and an external program. To run commands such as "20b", I'd need to synthesize "alt - left" 20 times in a row. Running something like `for i in $(seq 1 20); skhd -k "alt - left"` leads to considerable lag, as starting skhd 20 times incurs significant overhead.

Start by tracing skhd's command-line parsing for the existing -k and -t options, then follow the key-synthesis entry point. The issue describes repeated options within one invocation as the goal; done means multiple synthesized keypresses work without launching skhd repeatedly and preserve the current single-option behavior.

Written by the indexing model from the issue text.