feat(cli): add option to emit IR

[Wodann]

Adds the --emit-ir CLI flag to the build subcommand, for outputting LLVM IR to *.ll files instead of generating Mun libraries.

This PR also removes the need for #[serial] tests by adding and using a path input argument for the init and new subcommands, for deterministic execution of tests - in parallel.

[codecov]

Codecov Report

Merging #296 (44dfb04) into master (30bfe19) will increase coverage by 0.02%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
+ Coverage   79.51%   79.54%   +0.02%     
==========================================
  Files         228      228              
  Lines       13425    13480      +55     
==========================================
+ Hits        10675    10722      +47     
- Misses       2750     2758       +8     

Impacted Files	Coverage Δ
crates/mun_codegen/src/code_gen.rs	100.00% <ø> (ø)
crates/mun_codegen/src/code_gen/object_file.rs	100.00% <ø> (ø)
crates/mun_compiler/src/diagnostics_snippets.rs	84.00% <ø> (ø)
crates/mun_compiler/src/driver/config.rs	100.00% <ø> (ø)
crates/mun_compiler/src/lib.rs	71.05% <ø> (ø)
crates/mun/src/ops/init.rs	90.47% <50.00%> (-9.53%)	⬇️
crates/mun_compiler/src/db.rs	47.05% <50.00%> (ø)
crates/mun_codegen/src/assembly.rs	90.24% <87.09%> (-9.76%)	⬇️
crates/mun_compiler/src/driver.rs	64.28% <88.00%> (+2.48%)	⬆️
crates/mun/src/lib.rs	88.57% <100.00%> (+0.69%)	⬆️
... and 6 more

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[baszalmstra]

Nice and clean! 👍