feat: use extern functions in dispatch table

[baszalmstra]

This adds dynamic linking of malloc through the dispatch table. The use of malloc is still hacked in the runtime but this allows us to integrate all PRs that require it.

[codecov]

Codecov Report

Merging #90 into master will decrease coverage by 0.29%.
The diff coverage is 80.74%.

@@            Coverage Diff            @@
##           master      #90     +/-   ##
=========================================
- Coverage   74.63%   74.33%   -0.3%     
=========================================
  Files         117      119      +2     
  Lines        8893     9199    +306     
=========================================
+ Hits         6637     6838    +201     
- Misses       2256     2361    +105

Impacted Files	Coverage Δ
crates/mun_codegen/src/db.rs	100% <ø> (ø)	⬆️
crates/mun_runtime/src/test.rs	96.29% <ø> (-0.6%)	⬇️
crates/mun_runtime/src/assembly.rs	73.8% <0%> (+1.71%)	⬆️
crates/mun_runtime/src/macros.rs	25.64% <100%> (-0.68%)	⬇️
crates/mun_runtime/src/lib.rs	82.75% <100%> (+5.65%)	⬆️
crates/mun_codegen/src/ir/body.rs	90.02% <100%> (-0.18%)	⬇️
crates/mun_codegen/src/intrinsics/macros.rs	100% <100%> (ø)
crates/mun_codegen/src/ir.rs	50% <42.85%> (-30%)	⬇️
crates/mun_codegen/src/type_info.rs	56.09% <56.09%> (ø)
crates/mun_codegen/src/ir/dispatch_table.rs	90.97% <89.74%> (-1.63%)	⬇️
... and 26 more

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[Wodann]

Nice work! A very clean and minimal implementation.

It might be good to add unit tests for all of the different types that can be input as intrinsic arguments and return types.

[Wodann]

Enable adding mun alien functions to the dispatch table so we can use runtime linking for build-ins