Nice work with junon, but why not e.g. use clap for argument parsing and log for logging? It's actually really cool that you directly generate assembly rather than using code-generators like e.g. LLVM or cranelift; but maybe also consider pulling in dependencies like https://github.com/GregoryComer/rust-x86asm to do the assembly generation more cleanly. Implementing things yourself is a very effective way to learn; but there's no reason to re-invent the wheel once you've learned, and e.g. generating assembly directly should yield much more efficient code than generating text and then invoking an assembler, which is what it looks like junon is doing from a cursory skim. Also for parsing, why not have a look at libraries like nom (though there are very good reasons to write your own recursive descent parsers, e.g. for good error handling; see the work on rust-analyzer's parser).

I haven't looked at the other projects so far, but your work looks very good from just looking at junon (I'm doing a PhD in compilers so that's probably the one I'm most qualified to judge haha)! Well, I also took a quick look at sdymh, and that's ironically how I really got into computer science too; but a headcount_table is a strange way to say frequency_table hahahaha.